Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Open Quaternary”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

552 records · Page 31Linked to original sources
USGS2001

Density and velocity relationships for digital sonic and density logs from coastal Washington and laboratory measurements of Olympic Peninsula mafic rocks and greywackes

Three-dimensional velocity models for the basins along the coast of Washington and in Puget Lowland provide a means for better understanding the lateral variations in strong ground motions recorded there. We have compiled 16 sonic and 18 density logs from 22 oil test wells to help us determine the geometry and physical properties of the Cenozoic basins along coastal Washington. The depth ranges sampled by the test-well logs fall between 0.3 and 2.1 km. These well logs sample Quaternary to middle Eocene sedimentary rocks of the Quinault Formation, Montesano Formation, and Hoh rock assemblage. Most (18 or 82%) of the wells are from Grays Harbor County, and many of these are from the Ocean City area. These Grays Harbor County wells sample the Quinault Formation, Montesano Formation, and frequently bottom in the Hoh rock assemblage. These wells show that the sonic velocity and density normally increase significantly across the contacts between the Quinault or the Montesano Formations and the Hoh rock assemblage. Reflection coefficients calculated for vertically traveling compressional waves from the average velocities and densities for these units suggest that the top of the Hoh rock assemblage is a strong reflector of downward-propagating seismic waves: these reflection coefficients lie between 11 and 20%. Thus, this boundary may reflect seismic energy upward and trap a substantial portion of the seismic energy generated by future earthquakes within the Miocene and younger sedimentary basins found along the Washington coast. Three wells from Jefferson County provide data for the Hoh rock assemblage for the entire length of the logs. One well (Eastern Petroleum Sniffer Forks #1), from the Forks area in Clallam County, also exclusively samples the Hoh rock assemblage. This report presents the locations, elevations, depths, stratigraphic, and other information for all the oil test wells, and provides plots showing the density and sonic velocities as a function of depth for each well log. We also present two-way traveltimes for 15 of the wells calculated from the sonic velocities. Average velocities and densities for the wells having both logs can be reasonably well related using a modified Gardner’s rule, with p=1825v(1/4), where p is the density (in kg/m3) and v is the sonic velocity (in km/s). In contrast, a similar analysis of published well logs from Puget Lowland is best matched by a Gardner’s rule of p=1730v(1/4), close to the p=1740v(1/4) proposed by Gardner et al. (1974). Finally, we present laboratory measurements of compressional-wave velocity, shear-wave velocity, and density for 11 greywackes and 29 mafic rocks from the Olympic Peninsula and Puget Lowland. These units have significance for earthquake-hazard investigations in Puget Lowland as they dip eastward beneath the Lowland, forming the “bedrock” beneath much of the lowland. Average Vp/Vs ratios for the mafic rocks, mainly Crescent Formation volcanics, lie between 1.81 and 1.86. Average Vp/Vs ratios for the greywackes from the accretionary core complex in the Olympic Peninsula show greater scatter but lie between 1.77 and 1.88. Both the Olympic Peninsula mafic rocks and greywackes have lower shear-wave velocities than would be expected for a Poisson solid (Vp/Vs=1.732). Although the P-wave velocities and densities in the greywackes can be related by a Gardner’s rule of p=1720v(1/4), close to the p=1740v(1/4) proposed by Gardner et al. (1974), the velocities and densities of the mafic rocks are best related by a Gardner’s rule of p=1840v(1/4). Thus, the density/velocity relations are similar for the Puget Lowland well logs and greywackes from the Olympic Peninsula. Density/velocity relations are similar for the Washington coastal well logs and mafic rocks from the Olympic Peninsula, but differ from those of the Puget Lowland well logs and greywackes from the Olympic Peninsula.

Washington↗
USGS1970

Mineral resources of the southern half of Zone III Santander, Norte de Santander and Boyaca, Colombia

The areas covered by this report lies in the eastern Cordillera of the Colombian Andes in the region around Bucaramanga. This part of the eastern Cordillera consists of a structurally complex core of metamorphic and igneous rocks of Precambrian to Mesozoic age, flanked to east and west by faulted and folded sedimentary strata of late Paleozoic to Tertiary age. Infaulted blocks of sedimentary rocks are locally present in the massif. Unconsolidated deposits of Quaternary age, primarily terraced alluvium, are 10cally extensive in valleys on the flanks of the range. The crystalline central core of the range is called the Santander massif. In it are located the principal sold deposits and scattered deposits of copper, lead, zinc, and fluorite. The sedimentary rocks flanking the massif contain significant deposits of phosphate rock and gypsum, as well as other nonmetallic industrial minerals such as limestone, barite, glass sand, and coal. A belt of lead-zinc prospects in carbonate and sandstone beds of Cretaceous age on the east side of the range warrants further investigation. Gold and silver are the only important metallic minerals that have been produced in the Santander massif. Mining dates back to colonial and possibly to pre-colonial times and continues on a small scale at present. The California and Vetas district was the main area of investigation of metallic minerals during the present project. Results of geochemical sampling of stream sediments and assays of vein material indicate that the main potential of the area is in gold with lesser potentials in copper, lead, zinc, and silver. Mineralization of the district is probably younger than Early Cretaceous. Although no copper minerals have been mined elsewhere in the massif, small amounts of copper minerals in various rocks in scattered areas is revealed by green and blue stains of copper carbonates and sulfates. Deposits of greatest areal extent are in arkosic conglomeratic beds of the Giron Formation. These are being explored and sampled at the present time (1969). A little lead has been mined and smelted in the past but operations were on a very small scale and of short duration. Small amounts of lead, zinc, and copper minerals accompany dolomite replacement of Cretaceous limestone in a few scattered places, and several promising prospects are being investigated by means of trenches and drilling. One magnetite and several hematite prospects were examined but none offers any potential for economic development. Thick beds of gypsum in Lower Cretaceous limestone on Mesa de Los Santos, south of Bucaramanga are being quarried from outcrops for use in cement manufacture. The deposit was discovered shortly before the present project began, and although its extent beneath overlying strata is not yet determined by drilling, it appears to be in a small evaporite basin of about three kilometers in radius. Reserves of gypsum are large, but future development will have to be by underground mining. Outcrops of Cretaceous limestone of high purity are widespread and are more than adequate to meet all demands, which at present are for cement and calcined lime, road construction material, and to a small extent for agricultural lime and polished decorative stone. Upper Paleozoic limestone of the Diamante Formation crops out in a few places; it has been used near Bucaramanga for cement manufacture. Marble is present in several localities of the Santander massif in Lower Paleozoic and Devonian rocks. Impurities, fractures, and solution cavities render most of it unsuitable for decorative purposes, but selected parts are used in floor tile and terrazo. Recrystallized limestone of the Diamante Formation in the same area, usually referred to as marble, is of uniform high purity throughout a thick and uninterrupted section, and offers a good source of limestone raw material. A little is now used for agricultural lime. The potential of this resource has not been fully evalua

Open-File Report↗
USGS2015

California State Waters map series — Offshore of Pigeon Point, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The Offshore of Pigeon Point map area is located in central California, on the Pacific Coast about 50 km south of San Francisco and 25 km northwest of Santa Cruz. The onshore part of the map area is sparsely populated. The nearest significant onshore cultural center is Pescadero, an unincorporated community with a population of well under 1,000. The hilly coastal area is virtually undeveloped, used primarily for agricultural or as grazing land for sheep and cattle. Agriculture is limited to the coastal uplifted Pleistocene marine terraces and upper Pleistocene alluvial fan deposits, which lie between the shoreline and the northwest-trending Santa Cruz Mountains. The map area is cut by the San Gregorio Fault Zone, and is located a few kilometers southwest of the San Andreas Fault Zone. Coastal uplift and folding in the map area has been attributed to a westward bend in the San Andreas Fault Zone and also to right-lateral movement along the San Gregorio Fault Zone. The irregular coastal geomorphology of this area, which consists of low, rocky cliffs and sparse, small pocket beaches backed by low, terraced hills, is partly attributable to this ongoing deformation. The shelf in the map area is underlain by variable amounts (0 to 20 m) of upper Quaternary nearshore and shelf sediments deposited as sea level fluctuated in the late Pleistocene. The southern part of the map is characterized by the presence of uplifted bedrock that has been linked to a local zone of transpression in the San Gregorio Fault Zone. This uplift, coupled with high wave energy, has resulted in little or no sediment cover in this area where exposures of bedrock are present at water depths of as much as 45 m. The thickest deposits of sediment are located in the northern part of the map area. Coastal sediment transport in the map area is characterized by north-to-south littoral transport of sediment that is derived mainly from streams in the Santa Cruz Mountains and also from local coastal erosion. Shoreline-change studies indicate long-term erosion; within the region between San Francisco and Davenport, the highest long- and short-term coastal-erosion rates occur in the map area, just north of Point Año Nuevo. During the last approximately 300 years, as much as 18 million cubic yards (14 million cubic meters) of sand-sized sediment has been eroded from the area between Año Nuevo Island and Point Año Nuevo and transported south. Once widened by this pulse of eroded sediment, beaches south of Point Año Nuevo are now narrowing as the tail end of this mass of sand progresses farther south. The Offshore of Pigeon Point map area lies within the cold-temperate biogeographic zone that is called either the “Oregonian province” or the “northern California ecoregion.” This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, the eastern limb of the North Pacific subtropical gyre that flows from southern British Columbia to Baja California. At its midpoint off central California, the California Current transports subarctic surface (0–500 m deep) waters southward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception (about 335 km south of the map area), although its associated phylogeographic group of marine fauna may extend beyond to the area offshore of Los Angeles in southern California. The ocean off of central California has experienced a warming over the last 50 years that is driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical environment. Seafloor habitats in the Offshore of Pigeon Point map area lie within the Shelf (continental shelf) megahabitat. Significant rocky outcrops, which support kelp-forest communities in the nearshore and rocky-reef communities in deeper water, dominate the inner shelf waters. Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. Common fish species found in the kelp beds and rocky reefs include lingcod and various species of rockfish and greenling.

California↗
USGS1945

Ground-water conditions in the vicinity of Carlsbad, New Mexico

The area included in this investigation lies in Eddy County, New Mexico, largely between the foothills of the Guadalupe Mountains on the west and the Pecos River on the east, and extends from Carlsbad southward to Black River. The Pecos River drains the entire area, and in the growing season when water is diverted at Avalon Dam for irrigation its flow in this locality is maintained largely by the numerous springs emerging in the river channel north of Carlsbad. Carlsbad and vicinity depend on ground water fro a domestic water supply as the waters of the Pecos River are too highly mineralized for domestic use. About 1,120 acres of land was irrigation by ground water in the vicinity of Carlsbad in 1940. Valley fill, of Quaternary age, extends over most of the area, largely as a thin veneer, but it has a maximum known thickness of 256 feet. It is made up largely of clay with lenses of conglomerate, gravel, and sand. The Rustler formation, of upper Permian age, underlies the fills and is composed of gypsum and red beds with one persistent bed of limestone. The Salado formation, which is composed chiefly of halite (common salt), underlies the Rustler formation elsewhere buy it is absent over most of the area described in this paper. This Castile formations, which is predominantly anhydrite, underlies the Salado and overlies the Delaware Mountain group, of middle Permian age, which is deeply buried in most of the area. The upper part of the Delaware Mountain group grades into the Capitan and Carlsbad limestones to the north, east, and west, the latter being exposed near Carlsbad and in the foothills of the Guadalupe Mountain. The Carlsbad limestone in turn grades into the upper part of the Chalk Bluff formation. Ground water apparently moves eastward from the Guadalupe Mountains through the Carlsbad limestone to recharge the aquifers in the Delaware Mountain, Castile, and Salado units. In these formations the water soon becomes too highly mineralized for domestic or irrigation use. A large part of the water in the Carlsbad limestone emerges in the spring area north of Carlsbad, and a part of it moves into the valley fill in Dark Canyon Arroyo. The water in the fill of Dark Canyon Arroyo moves laterally into the limestone of the Rustier formation. The water moving eastward in the valley fill and Rustier limestone becomes progressively more mineralized and in the farmland area in the Carlsbad Irrigation Dstrict it is unfit for domestic use. In addition, highly mineralized water seeping from the farmlands and canals in the Carlsbad Irrigation District commingles with the water from the west, and the resulting mixture is undesirable even for watering stock, although if necessity it is much used for that purpose. Water occurs in channels of the Carlsbad limestone, and wells drilled into it generally obtain large yields id hard but potable water. The municipal supply of the city of Carlsbad is derived from 4 wells (1940) in the Carlsbad limestone. The aquifer has a high transmissibility in the vicinity of Carlsbad, as was shown by a test made on one of the wells owned by Southwestern Public Service Co. This well has a specific capacity of 275 gallons per minute per foot of drawdown. The present withdrawal of water from wells penetrating the aquifers in the Carlsbad limestone averages about 4 second-feet (about 2,600,00 gallons a day). The average flow emerging in the spring area in the Pacos River north of Carlsbad is about 60 second-feet (about 40 million gallons a day). It appears that about 12 second-feet of this flow (about 8 million gallons a day) comes from aquifers in the Carlsbad limestone and that the remainder represents leakage from Lake Avalon and the canal system. The valley fill is less permeable than the Carlsbad limestone but in some places sufficient yields are obtained for irrigation purposes. A test made on a well in the fill just south of Carlsbad showed the aquifer in that locality to have a transmissibility of about 60,000. Contamination of the household wells in West Carlsbad does not appear to be taking place at the present time although the juxtaposition of cesspools and outhouses on the one hand and poorly cased wells for domestic water supply on the other makes the situation dangerous.

New Mexico↗
USGS2001

Surficial geology of the lower Comb Wash, San Juan County, Utah

The surficial geologic map of lower Comb Wash was produced as part of a master’s thesis for Northern Arizona University Quaternary Sciences program. The map area includes the portion of the Comb Wash alluvial valley between Highway 163 and Highway 95 on the Colorado Plateau in southeastern Utah. The late Quaternary geology of this part of the Colorado Plateau had not previously been mapped in adequate detail. The geologic information in this report will be useful for biological studies, land management and range management for federal, state and private industries. Comb Wash is a south flowing ephemeral tributary of the San Juan River, flanked to the east by Comb Ridge and to the west by Cedar Mesa (Figure 1). The nearest settlement is Bluff, about 7 km to the east of the area. Elevations range from 1951 m where Highway 95 crosses Comb Wash to 1291 m at the confluence with the San Juan River. Primary vehicle access to lower Comb Wash is provided by a well-maintained dirt road that parallels the active channel of Comb Wash between Highway 163 and Highway 95. For much of the year this road can be traversed without the aid of four-wheel drive. However, during inclement weather such as rain or snow the road becomes treacherous even with four-wheel drive. The Comb Wash watershed is public land managed by the Bureau of Land management (BLM) office in Monticello, Utah. The semi-arid climate of Comb Wash and the surrounding area is typical of the Great Basin Desert. Temperature in Bluff, Utah ranges from a minimum of –8° C in January to a maximum of 35° C in July with a mean annual temperature of 9.8° C (U.S. Department of Commerce, 1999). The difference between day and nighttime temperatures is as great as 20° C. Between 1928 and 1998, annual rainfall in Bluff averaged 178 mm per year (U.S. Department of Commerce, 1999). Annual rainfall in Comb Wash averaged 240 mm per year from 1991 to 1999 while Bluff received an average of 193 mm for the same 8 year period. Most precipitation is monsoonal, convective storms that bring moisture from the Gulf of Mexico beginning in early July and ending by October. Large frontal storms during December and January are responsible for most winter precipitation (Figure 2). The record from U.S. Geological Survey gauging station number 09379000 operated by the BLM from 1959 through 1968 indicates that Comb Wash flows in direct response to precipitation events. Most daily discharge and peak events occur in late July through September, coinciding with high intensity monsoon thunderstorms. Comb Wash supports a variety of vegetation typical of the Great Basin Desert and the northern desert shrub zone as described by Fowler and Koch (1982). On the lower alluvial terraces, bushes and shrubs dominate the vegetation, including: sagebrush (Artemesia tridentata), rabbitbrush (Chrysothamnus nauseosus), fourwing saltbush (Atriplex canescens), winterfat (Eurotia lanata), greasewood (Sarcobatus vermiculatus), and shadscale (Atriplex concertifolia). Juniper trees (Juniperus osteosperma) can be found on the rocky colluvial slopes near Comb Ridge and on the higher terrace near Cedar Mesa. The floodplain contains an abundance of riparian vegetation including cottonwood (Populus fremontii), willow (Salix exigua), and tamarisk (Tamarix ramosissima). Tamarisk is one of 7 non-native species present in the lower Comb Wash watershed. At least seven known species of noxious weeds have invaded the watershed, including Bermuda grass (Cynodon dactylon), field bindweed (Convolvulus avensis), Canada thistle (Cirsium arvense), Russian knapweed (Centaurea repens), tamarisk and camel thorn (Alhagi pseudalhagi). Of these, tamarisk or salt-cedar has most aggressively colonized the southwestern United States, including the San Juan watershed. Graf (1978) estimates that since the late 19th century, tamarisk has spread at a rate of 20 km per year. Tamarisk first appeared in Comb Wash during the mid to early 20th century based on photographs taken by Gregory in the early 1900’s (Gregory, 1938).

Utah↗
USGS2002

Post-glacial inflation-deflation cycles, tilting, and faulting in the Yellowstone Caldera based on Yellowstone Lake shorelines

The Yellowstone caldera, like many other later Quaternary calderas of the world, exhibits dramatic unrest. Between 1923 and 1985, the center of the Yellowstone caldera rose nearly one meter along an axis between its two resurgent domes (Pelton and Smith, 1979, Dzurisin and Yamashita, 1987). From 1985 until 1995-6, it subsided at about two cm/yr (Dzurisin and others, 1990). More recent radar interferometry studies show renewed inflation of the northeastern resurgent dome between 1995 and 1996; this inflation migrated to the southwestern resurgent dome from 1996 to 1997 (Wicks and others, 1998). We extend this record back in time using dated geomorphic evidence of postglacial Yellowstone Lake shorelines around the northern shore, and Yellowstone River levels in the outlet area. We date these shorelines using carbon isotopic and archeological methods. Following Meyer and Locke (1986) and Locke and Meyer (1994), we identify the modern shoreline as S1 (1.9 ? 0.3 m above the lake gage datum), map paleoshoreline terraces S2 to S6, and infer that the prominent shorelines were cut during intracaldera uplift episodes that produced rising water levels. Doming along the caldera axis reduces the gradient of the Yellowstone River from Le Hardys Rapids to the Yellowstone Lake outlet and ultimately causes an increase in lake level. The 1923-1985 doming is part of a longer uplift episode that has reduced the Yellowstone River gradient to a ?pool? with a drop of only 0.25 m over most of this 5 km reach. We also present new evidence that doming has caused submergence of some Holocene lake and river levels. Shoreline S5 is about 14 m above datum and estimated to be ~12.6 ka, because it post-dates a large hydrothermal explosion deposit from the Mary Bay area (MB-II) that occurred ~13 ka. S4 formed about 8 m above datum ~10.7 ka as dated by archeology and 14C, and was accompanied by offset on the Fishing Bridge fault. About 9.7 ka, the Yellowstone River eroded the ?S-meander?, followed by a ~5 m rise in lake level to S2. The lowest generally recognizable shoreline is S2. It is ~5 m above datum (3 m above S1) and is ~8 ka, as dated on both sides of the outlet. Yellowstone Lake and the river near Fishing Bridge were 5-6 m below their present level about 3-4 ka, as indicated by 14C ages from submerged beach deposits, drowned valleys, and submerged Yellowstone River gravels. Thus, the lake in the outlet region has been below or near its present level for about half the time since a 1 km-thick icecap melted from the Yellowstone Lake basin about 16 ka. The amplitude of two rises in lake and river level can be estimated based on the altitude of Le Hardys Rapids, indicators of former lake and river levels, and reconstruction of the river gradient from the outlet to Le Hardys Rapids. Both between ~9.5 ka and ~8.5 ka, and after ~3 ka, Le Hardys Rapids (LHR) was uplifted about 8 meters above the outlet, suggesting a cyclic deformation process. Older possible rises in lake level are suggested by locations where the ~10.7 ka S4 truncates older shorelines, and valleys truncated by the ~12.6 ka S5 shoreline. Using these controls, a plot of lake level through time shows 5-7 millennial-scale oscillations since 14.5 ka. Major cycles of inflation and deflation are thousands of years long. Le Hardys Rapids has twice been uplifted ~8 m relative to the lake outlet. These two locations span only the central 25% of the historic caldera doming, so that if we use historic doming as a model, total projected uplift would be ~32 m. This ?heavy breathing? of the central part of the Yellowstone caldera may reflect a combination of several possible processes: magmatic inflation, tectonic stretching and deflation, and hydrothermal fluid sealing and inflation followed by cracking of the seal, pressure release, and deflation. Over the entire postglacial period, subsidence has balanced or slightly exceeded uplift as shown by older shorelines that descend towards the caldera axis. We

Open-File Report↗
USGS2002

Physical data of soil profiles formed on late Quaternary marine terraces near Santa Cruz, California

The marine terraces in and around Santa Cruz, California, represent a set of well-preserved terraces formed as a product of geology, sea level, and climate. A marine terrace begins as a wave cut platform. Eustatic sea level changes, seacliff erosion, and tectonic uplift work together to generate marine terraces. "When a wave-cut platform is raised (due to tectonic activity) above sea level and cliffed by wave action it becomes a marine terrace" (Bradley, 1957, p. 424). During glacial periods, eustatic sea level is estimated to have dropped by 150 meters (Fairbanks, 1989). Cliff retreat measured from aerial photographs between 1930 and 1980 vary from 0.0 to 0.2 m yr–1 (Best and Griggs, 1991). Estimates of uplift rates along the Santa Cruz coastline vary from 0.10 to 0.48 m kyr–1 (Bradley and Griggs, 1976; Weber and others, 1999). Uplift mechanisms include coseismic uplift associated both with a reverse component of slip on the steeply SW dipping Loma Prieta fault in the restraining bend of the San Andreas Fault and a small component of reverse slip on the steeply SE dipping San Gregorio fault (Anderson and Menking 1994). Previous work studying physical properties on these terraces include Pinney and others (in press) and Aniku (1986) and Bowman and Estrada (1980). Sedimentary deposits of the marine terraces are a mixture of terrestrial and marine sediments but generally consist of a sheet of marine deposits overlying the old platform and a wedge of nonmarine deposits banked against the old sea cliff (Bradley, 1957). Bedrock underlying the terraces in the Santa Cruz area is generally either Santa Margarita Sandstone or Santa Cruz Mudstone. The Santa Margarita Sandstone represents an upper Miocene, transgressive, tidally dominated marine-shelf deposit with crossbedded sets of sand and gravel and horizontally stratified and bioturbated invertebrate-fossils beds (Phillips, 1990). The siliceous Santa Cruz Mudstone, of late Miocene age, conformably overlies the Santa Margarita Sandstone. The Santa Cruz Mudstone is a thin to medium-bedded siliceous mudstone with nonsiliceous mudstone and siltstone and minor amounts of sandstone. The siliceous nature implies organic deposition in a quiescent, deep-water environment. Bedrock is mantled by 1–4 meters of medium to coarse-grained regressive beach sediment and fluvial deposits from the Ben Lomond Mountains. Terrace age increases with elevation above sea level, and weathering of primary minerals increases with age. The suite of soils formed on the terraces is referred to as a soil chronosequence. Soil chronosequences, important tools in characterizing natural weathering rates, are defined as a group of soils that differ in age and therefore in duration of weathering but have similar climatic conditions, vegetation, geomorphic position, and parent material (Jenny, 1941; Birkland, 1999). Soils are frequently useful indicators of geomorphic age (Muhs, 1982; Switzer and others, 1988) and are a function of pedogenic and/or eolian processes. Some aspects of soil development can be episodic but when viewed on large time scales can be perceived as continuous (Switzer and others, 1988). The age of the soil may be constrained by the age of the deposit, since soil formation generally commences when deposition has ceased (Birkland, 1999). Dating of the terraces provides an unprecedented opportunity to study weathering and soil-formation rates (Perg and others, 2001; Hanks and others, 1984; Bradley and Griggs, 1976; Bradley and Addicott, 1968; Bradley, 1956). Ages of the terraces recently dated by cosmogenic radionuclide are, starting with the youngest, 65, 92, 137, 139, and 226 k.y. (Perg and others, 2001). However, these ages are much younger than recent radiometric dates on mollusk shells (Muhs, U.S. Geological Survey, personal communication, 2002; Bradley and Addicott, 1968). For this study, soils were sampled on five terraces. Terrace one in the Lighthouse Field along Westcliff in Santa Cruz was the last site selected, and this report contains minimal data on this terrace. Sites on the second, third, and fourth terraces are located in Wilder Ranch, Santa Cruz, California. Site five is on private property north of Wilder Ranch. Careful consideration was taken in selecting field sites, choosing locations in a topographically flat area to avoid effects of erosion, and trying to keep parent material similar. This report contains physical properties of the soil profiles on four of the five marine terraces near Santa Cruz, California, excluding the youngest terrace in all tables except 6 and 7. Data includes field descriptions, bulk density, grain size analyses, weight percent magnetic fraction, and the soil development index. Soil properties are important when trying to understand the chemistry of a given profile or when comparing profiles. Grain size constrains the movement of water in a profile, thus controlling movement of chemicals and weathering rates. Bulk density is a useful property to calculate chemical inventory. Quantifying the magnetic fraction aids in understanding the Fe inventory for these soils. The soil development index is a semi-quantitative way to define the degree of development of a soil profile. This is a useful way to compare development of profiles for this chronosequence or compare the Santa Cruz terraces to a suit of other terraces or another chronosequence.

California↗
USGS1996

Summary of the Snake River plain Regional Aquifer-System Analysis in Idaho and eastern Oregon

Regional aquifers underlying the 15,600-square-mile Snake River Plain in southern Idaho and eastern Oregon was studied as part of the U.S. Geological Survey's Regional Aquifer-System Analysis program. The largest and most productive aquifers in the Snake River Plain are composed of Quaternary basalt of the Snake River Group, which underlies most of the 10,8000-square-mile eastern plain. Aquifer tests and simulation indicate that transmissivity of the upper 200 feet of the basalt aquifer in the eastern plain commonly ranges from about 100,000 to 1,000,000 feet squared per day. However, transmissivity of the total aquifer thickness may be as much as 10 million feet squared per day. Specific yield of the upper 200 feet of the aquifer ranges from about 0.01 to 0.20. Average horizontal hydraulic conductivity of the upper 200 feet of the basalt aquifer ranges from less than 100 to 9,000 feet per day. Values may be one to several orders of magnitude higher in parts in individual flows, such as flow tops. Vertical hydraulic conductivity is probably several orders of magnitude lower than horizontal hydraulic conductivity and is generally related to the number of joints. Pillow lava in ancestral Snake River channels has the highest hydraulic conductivity of all rock types. Hydraulic conductivity of the basalt decreases with depth because of secondary filling of voids with calcite and silica. An estimated 80 to 120 million acre-feet of water is believed to be stored in the upper 200 feet of the basalt aquifer in the eastern plain. The most productive aquifers in the 4,800-square-mile western plain are alluvial sand and gravel in the Boise River valley. Although aquifer tests indicate that transmissivity of alluvium in the Boise River valley ranges from 5,000 to 160,000 feet squared per day, simulation suggests that average transmissivity of the upper 500 feet is generally less than 20,000 feet squared per day. Vertically averaged horizontal hydraulic conductivity of the upper 500 feet of alluvium ranges from about 4 to 40 feet per day; higher values can be expected in individual sand and gravel zones. Vertical hydraulic conductivity is considerably lower because of the presence of clay layers. Hydraulic heads measured in piezometers, interpreted from diagrams showing ground-water flow and equipotential lines and estimated by computer simulation, demonstrate that water movement is three dimensional through the rock framework. Natural recharge takes place along the margins of the plain where head decreases with depth; discharge takes place near some reaches of the Snake River and the Boise River where head increases with depth. Geothermal water in rhyolitic rocks in the western plain and western part of the eastern plain has higher hydraulic head than the overlying cold water. Geothermal water, therefore, moves upward and merges into the cold-water system. Basin water-budget analyses indicate that the volume of cold water. Carbon-14 age determinations, which indicate that residence time of geothermal water is 17,700 to 20,300 years, plus or minus 4,000 years, imply slow movement of water through the geothermal system. Along much of its length, the Snake River gains large quantities of ground water. On the eastern plain, the river gained about 1.9 million acre-feet of water between Blackfoot and Neeley, Idaho, in 1980. Between Milner and King Hill, Idaho, the river gained 4.7 million acre-feet, mostly as spring flow from the north side. Upstream from Blackfoot and in the vicinity of Lake Walcott, the rover loses flow to ground water during parts or all of the year. On the western plain, river gains from ground water are small relative to those on the eastern plain; most are from seepage. Streams in tributary drainage basins supply calcium/bicarbonate type and calcium/magnesium/bicarbonate type water to the plain. Water type is a reflection of the chemical composition of rocks in the drainage basin, Concentrations of dissolved solids are smallest, about 50 milligrams per liter, in streams such as the Boise River that drain areas of granitic rocks; concentrations are greatest, about 400 milligrams per liter, in streams such as the Owyhee and Raft Rivers that drain area of sedimentary rocks. Water chemistry reflects the interaction of surface water and ground water. The chemical composition of ground water in the plain is essentially the same as that in streamflow and groundwater discharge from tributary drainage basins. Tributary drainage basins supplied 85 percent of the ground-water recharge in the eastern plain during 1980 and a nearly equivalent percentage of the solute load in ground water; human activities and dissolution of minerals supplied the other solutes. Dissolved-solids concentrations in ground water were generally less than 400 milligrams per liter. Water from the lower geothermal system is chemically different from water from the upper cold-water system. Geothermal water typically has greater concentrations of sodium, bicarbonate, sulfate, chloride, fluoride, silica, arsenic, boron, and lithium and smaller concentrations of calcium, magnesium, and hydrogen. Difference are attributed to ion exchange as geothermal moves through the rock framework. Irrigation, mostly on the Snake River Plain, accounted for about 96 percent of consumptive water use in Idaho during 1980. The use of surface water for irrigation for more than 100 years has caused major changes in the hydrologic system on the plain. Construction of dams, reservoirs, and diversifications effected planned changes in the surface-water system but resulted in largely unplanned changes in the ground-water system. During those years of irrigation, annual recharge in the main part of the eastern plain increased to about 6.7 million acre-feet in 1980, or by about 70 percent. Most of the increase was from percolation of surface water diverted for irrigation. From preirrigation to 1952, groundwater storage increased about 24 million acre-feet, and storage decreased from 1952 to 1964 and from 1976 to 1980 because of below-normal precipitation and increased withdrawals of ground water for irrigation. Annual ground-water discharge increased to about 7.1 million acre-feet in 1980, or about 80 percent since the start of irrigation. About 10 percent of the 1980 total discharge was ground-water pumpage. About 3.1 million acres, or almost one-third of the plain, was irrigated during 1980: 2.0 million acres with surface water, 1.0 million acres with ground water, and 0.1 million acres with combined surface and ground water. About 8.9 million acre-feet of Snake River water was diverted for irrigation during 1980 and 2.3 million acre-feet of ground water was pumped from 5,300 wells. Most irrigation wells on the eastern plain are open to basalt. About two-thirds of them yield more than 1,500 gallons per minute with a reported maximum of 7,240 gallons per minute; drawdown is less than 20 feet in two-thirds of the wells. Most irrigation wells on the western plain are open to sedimentary rocks. About one-third of them yield more than 1,00 gallons per minute with a reported maximum of 3,850 gallons per minute; drawndown is less than 20 feet in about one-fifth of the wells. The major instream use of water on the Snake River Plain is hydroelectric power generation. Fifty-two million acre-feet of water generated 2.6 million megawatthours of electricity during 1980. Digital computer ground-water flows models of the eastern and western plain reasonably simulated regional changes in water levels and ground-water discharges from 1880 (preirrigation) to 1980. Model results support the concept of three-dimensional flow and the hypotheses of no underflow between the eastern and western plain. Simulation of the regional aquifer system in the eastern plain indicates that is 1980 hydrologic conditions, including pumpage, were to remain the same for another 30 years, moderate declines in ground-water levels and decreases in spring discharges would continue. Increased ground-water pumpage to irrigate an additional 1 million acres could cause ground-water levels to decline a few tens of feet in the central part of the plain and could cause corresponding decreases in ground-water discharge. A combination of actions such as increased ground-water pumpage and decreased use of surface water for irrigation (resulting in reduced recharge) would accentuate the changes.

Idaho;Oregon↗
USGS2016

California State Waters map series — Offshore of Aptos, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar bathymetric data (the undersea equivalent of satellite remote-sensing data in terrestrial mapping), acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The Offshore of Aptos map area is located on the Pacific Coast, on the north side of Monterey Bay, about 105 km southeast of San Francisco. The largest incorporated city in the map area, Capitola, and numerous unincorporated towns including Aptos, lie on uplifted marine terraces between the shoreline, and the northwest-trending Santa Cruz Mountains, part of California’s Coast Ranges. The map area includes the northernmost part of Santa Cruz Harbor, and Moss Landing Harbor is located about 10 km south of the map area. The offshore part of the map area is entirely within California’s State Waters and is also part of the Monterey Bay National Marine Sanctuary. In the southern part of the map area, the Soquel Canyon State Marine Conservation Area extends eastward from the limit of California’s State Waters across Soquel Canyon. The Offshore of Aptos map area is on the western margin of North American Plate—the only continental margin in the world delineated largely by transform faults. The San Andreas Fault Zone cuts through the Santa Cruz Mountains just 3.5 km northeast of the map area. The San Gregorio Fault Zone, another major plate-boundary structure, cuts through Monterey Canyon about 13 km southwest of the map area. Ongoing deformation associated with and between these major fault zones has uplifted the Santa Cruz Mountains and formed well-developed sets of marine terraces that characterize almost the entire coastal zone of the map area. The offshore part of the map area consists of relatively flat and shallow continental shelf which is underlain by variable amounts (0 to 30 m) of upper Quaternary shelf, estuarine, and fluvial sediments deposited as sea level fluctuated in the late Pleistocene. Along the southern edge of the map area, the shelf is incised by the head of Soquel Canyon, a northeast-trending tributary to the west-trending Monterey Canyon. During the last sea-level lowstand (the Last Glacial Maximum [LGM], about 21,000 years ago) Soquel Creek flowed through a paleochannel across the emergent shelf into the head of Soquel Canyon. This canyon was disconnected from its onshore watershed during the post-LGM sea-level rise of about 125 m; the abandoned paleochannel was subsequently filled with marine sediment. Coastal sediment in the Offshore of Aptos map area is supplied by coastal watersheds and bluff erosion. Sediment transport in this part of the Santa Cruz littoral cell is primarily from the northwest to the southeast and terminates in the submarine Monterey Canyon. Longshore drift is impeded by jetties at Santa Cruz Harbor, resulting in high beach erosion rates east of the harbor. Sediment dredged from the harbor mouth (estimated 300,000 yds 3 /yr) is currently being used to nourish beaches directly to the east. Farther downcoast, the rapidly eroding beach at Capitola was stabilized by construction of an about 75-m-long groin. This part of central California is exposed to large North Pacific swells from the northwest throughout the year. North Pacific swell heights range from 2 to 10 meters, with larger swells occurring from October to May. During El Niño-Southern Oscillation (ENSO) events, winter storms track farther south than they do in normal (non-ENSO) years, thereby impacting the map area more frequently and with waves of larger heights. Bedrock exposed in coastal cliffs is relatively erosion-resistant, and significant erosional events primarily are restricted to storm-wave activity that also erodes the overlying unconsolidated marine-terrace sediments. The Offshore of Aptos map area lies within the cold-temperate biogeographic zone that is called either the “Oregonian” province or the “northern California ecoregion.” This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, the eastern limb of the North Pacific subtropical gyre that flows from southern British Columbia to Baja California. At its midpoint off central California, the California Current transports subarctic surface (0–500 m deep) waters southward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception (about 310 km southeast of the map area), although its associated phylogeographic group of marine fauna may extend beyond to the area offshore of Los Angeles in southern California. The ocean off of central California has experienced a warming over the last 50 years that is driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical environment. Seafloor habitats in the Offshore of Aptos map area lie within the “Shelf” Megahabitat class and include patchy rocky habitats, gravel-rich scour depressions, minor bedrock habitat, and predominantly sandy inner shelf. Sandy shelf habitats grade offshore to mud-dominated habitats on the midshelf in deeper water. Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. California sea lions and Pacific harbor seals are abundant in the map area. Common bottlenose dolphins are often observed very close to shore and in the surf zone. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. The kelp beds are the northernmost known habitat for the population of southern sea otters. Common fish species found in the kelp beds and rocky reefs include blue rockfish, black rockfish, olive rockfish, kelp rockfish, gopher rockfish, black-and-yellow rockfish, painted greenling, kelp greenling, and lingcod.

California↗
USGS1991

Hydrology of the Texas Gulf Coast aquifer systems

A complex, multilayered ground-water flow system exists in the Coastal Plain sediments of Texas. The Tertiary and Quaternary clastic deposits have an areal extent of 114,000 square miles onshore and in the Gulf of Mexico. Two distinct aquifer systems are recognized within the sediments, which range in thickness from a few feet to more than 12,000 feet The older system--the Texas coastal uplands aquifer system-consists of four aquifers and two confining units in the Claiborne and Wilcox Groups. It is underlain by the practically impermeable Midway confining unit or by the top of the geopressured zone. It is overlain by the nearly impermeable Vicksburg-Jackson confining unit, which separates it from the younger coastal lowlands aquifer system. The coastal lowlands aquifer system consists of five permeable zones and two confining units that range in age from Oligocene to Holocene. The hydrogeologic units of both systems are exposed in bands that parallel the coastline. The units dip and thicken toward the Gulf. Quality of water in the aquifer systems is highly variable, with dissolved solids ranging from less than 500 to 150,000 milligrams per liter. Substantial withdrawal from the aquifer systems began in the early 1900's and increased nearly continuously into the 1970's. The increase in withdrawal was relatively rapid from about 1940 to 1970. Adverse hydrologic effects, such as saltwater encroachment in coastal areas, land-surface subsidence in the Houston-Galveston area, and long-term dewatering in the Whiter Garden area, were among some of the factors that caused pumping increases to slow or to cease in the 1970's and 1980's. Ground-water withdrawals in the study area in 1980 were about 1.7 billion gallons per day. Nearly all of the withdrawal was from four units: Permeable zones A, B, and C of Miocene age and younger, and the lower Claiborae-upper Wilcox aquifer. Ground-water levels have declined hundreds of feet in the intensively pumped areas of Houston-Galveston, Kingsville, Winter Garden, and Lufkin-Nacogdoches. Water-level declines have caused inelastic compaction of clays which, in turn, has resulted in land-surface subsidence of more than one foot in an area of about 2,000 square miles. Maximum subsidence of nearly 10 feet occurs in the Pasadena area east of Houston. A three-dimensional, variable-density digital model was developed to simulate predevelopment and transient flow in the aquifer systems. The modeled area is larger than the study area, and includes adjacent parts of Louisiana and Mexico. The transient model calibration period was from 1910 (predevelopment) to 1982. Model-generated head distributions, water-level hydrographs, and land-surface subsidence were matched to measured data in selected, intensively pumped areas. For the study area, mean horizontal hydraulic conductivity in the calibrated model ranges from 10 feet per day for the middle Wilcox aquifer to 25 feet per day for permeable zone A. Mean transmissivity ranges from about 4,600 feet squared per day for the middle Claiborne aquifer to about 10,400 feet squared per day for permeable zone D. Mean vertical hydraulic conductivity ranges from 1.1x10 -5 feet per day for the Vicksburg-Jackson confining unit, to 3.8x10 -3 feet per day for permeable zone A. Mean values of calibrated storage coefficient range from 52x10 -4 for the middle Claiborne aquifer to 1.7x10 -3 for the middle Wilcox aquifer and permeable zone C. Calibrated inelastic specific storage values for clay beds in permeable zones A, B, and C in the Houston-Galveston area are 8.5x10 -5 , 8.0x10 -5 , and 8.0x10 -6 feet -1 , respectively. These values are 85, 80, and 8 times greater than the estimated elastic specific storage value for the clays in permeable zones A, B, and C, respectively. Recharge rates were mapped for predevelopment conditions as determined from a steady-state model calibration. A maximum rate of 3 inches per year was simulated in small areas, and the average rate for the study area was 034 inch per year. Total simulated recharge was 85 million cubic feet per day in the outcrop area. Recharge was equal to discharge in outcrop areas (79 million cubic feet per day) plus net lateral flow out of the study area (6 million cubic feet per day). Rates of inflow and outflow to the ground-water system have nearly tripled from predevelopment to 1982 (85 to 276 million cubic feet per day) based on model simulation. Withdrawal of 231 million cubic feet per day was supplied principally by an increase in outcrop recharge and, to a lesser extent, from a decrease in natural discharge and release of water from storage in aquifers and compacting clay beds. The average simulated 1982 recharge rate for the study area was 0.52 inch per year, with a maximum simulated rate of 6 inches per year in Jackson and Wharton Counties. Because withdrawal has caused problems such as saltwater intrusion, land-surface subsidence, and aquifer dewatering, the Texas Department of Water Resources has projected that ground-water use will decline substantially in most of the study area by the year 2030. Some areas remain favorable for development of additional ground-water supplies. Pumping from older units that are farther inland and in areas where potential recharge is greater will minimize adverse hydrologic effects.

Texas↗
USGS1950

Geology and paleontology of the Santa Maria district, California

Stratigraphy, paleontology, and geologic history.-A basement' consisting of igneous rocks of the Jurassic(?) Franciscan formation and sediments of the Upper Jurassic Knoxville formation, and formations of Tertiary and Quaternary age are exposed in the Santa Maria district. The outcrop section, exclusive of the Franciscan, has a maximum thickness of about 10,000 feet, the subsurface section about 27,000 feet. At no locality, however, is either outcrop or subsurface section as thick as the total maxima for the formations. The outcrop Franciscan is made up of altered basalt, gabbro (generally- greatly altered), and minor areas of peridotite and serpentine. The marine Knoxville formation, consisting of shale, thin-bedded calcareous sandstone, and conglomerate, was deposited on the igneous rocks of the Franciscan. It has an outcrop thickness of about 500 feet and a known subsurface thickness of at least 1,250 feet. Aucella cf. A. piochii, which occurs in both outcrop and subsurface sections, suggests late Jurassic age. The Franciscan and Knoxville were probably uplifted during Taliaferro's Diablan orogeny at the close of the Jurassic and formed a land area that presumably endured during early Cretaceous and perhaps during much of late Cretaceous time. If sediments were laid down while 10,000 feet of Upper Cretaceous were deposited in the adjoining San Rafael Mountains, they were eroded following uplift at the close of the Cretaceous, when Reed and Hollister's San Rafael uplift was formed. The district is inferred to have been part of a Franciscan and Knoxville land area at the south border of the San Rafael uplift during all of early Tertiary time. The known history of the district as part of a Tertiary basin began in the early Miocene(?), possibly a little earlier or possibly 3: little later, when the nonmarine sediments of the early Miocene(?) Lospe formation were deposited. The Lospe formation has a maximum thickness of 2, 700 feet, and is made up of coarse-grained reddish sandstone and conglomerate, and greenish sandstone, gypsiferous siltstone, and mudstone. White tuff is a minor but conspicuous constituent. The Lospe formation overlies the Knoxville, or· overlaps it and rests on the Franciscan. The first known Tertiary invasion of the sea took place immediately thereafter in early middle Miocene time, and from then on until approximately the end of the Pliocene the sea occupied continuously at least most of the region. The extent of the Miocene basin is not certainly known, but it was part of an extensive· basin that has been designated the Santa Barbara embayment. The early middle Miocene Point Sal formation is the earliest marine Tertiary formation. It has an outcrop thickness of as much as 1,500 feet and a maximum subsurface thickness of 3,600 feet, and consists of siltstone, mudstone, and thin beds of sandstone. The Point Sal formation overlies the Lospe formation without marked discontinuity, or overlaps it and rests on Knoxville or Franciscan. It contains a large foraminiferal fauna representing the Siphogenerina hughesi zone, or the lower part of Kleinpell's Relizian stage. The Monterey shale overlies the Point Sal formation without noticeable discontinuity, or overlaps all the older sedimentary formations and rests on the Franciscan. It has a maximum outcrop thickness of 2,100 feet, but is as much as 5,000 feet thick in some subsurface sections. The Monterey is divided into three mapped members. The lower member is characterized by phosphatic shale and somewhat porcelaneous shale; the middle member by chert and cherty shale; and the upper member by porcelaneous shale, or by both porcelaneous shale and diatomaceous strata. The lower member contains Foraminifera representing the upper part of Kleinpell's Relizian stage and all of his Luisian stage, the middle member a few species indicating the lower part of his Mohnian stage, and the upper member a fauna representing the upper part of the Bolivina hughesi zone, at the top of the Mohnian, and in part a younger unnamed faunal division; that is, the Monterey is of late middle and late Miocene age. The diverse stratigraphic relations of the Lospe and Point Sal formations and Monterey shale along the borders of the Franciscan rocks forming Point Sal Ridge are inferred to be the result of repeated movements during Miocene time in the area of basement rocks west of the district, presumably extending westward beyond the present coast. Toward the close of the Miocene, low ridges appeared on the floor of the sea, ridges that grew during Pliocene time and were destined to become anticlines. At the same time deformation took place in the northeastern part of the district, and elsewhere on some anticlines, or on other structural highs bounded by faults. In those areas the Sisquoc formation overlies the Monterey shale with marked discordance; elsewhere there is no discordance. Two facies of the Sisquoc formation are mapped: a marginal sandstone facies, designated the Tinaquaic sandstone member, and a basin facies. The Tinaquaic sandstone member is 1,400 feet thick and contains megafossils of middle Pliocene age (also early Pliocene just east of the mapped area). It is unconformable on the Monterey. The basin facies, at least 3,000 feet thick in outcrop sections and 5,000 in some subsurface sections, consists of diatomaceous mudstone, other types of diatomaceous ·strata, somewhat porcelaneous mudstone, and porcelaneous shale-deposits that are ordinarily characteristic of the Monterey shale. Even in areas where the two formations are lithologically indistinguishable and conformable, a field basis for differentiating them has been established. The basin facies of the Sisquoc conformably overlies the Monter.ey in outcrop sections, but in some subsurface sections the formations are unconformable, and on the north limb of the Santa Maria Valley syncline the basin facies of the Sisquoc overlaps the Monterey onto the basement, thus forming the overlap trap for the oil in the Monterey in the Santa Maria Valley field. The lower and middle parts of the basin facies contain Foraminifera of the Bolivina obliqua zone. Kleinpell assigned that zone to the lower part of his late upper Miocene Delmontian stage. Assignment to the upper Delmontian, however, appears to be preferable. The upper few hundred feet of the basin facies contain Foraminifera similar to those in the overlying Foxen mudstone and megafossils of middle Pliocene affinities. The basin facies is therefore considered late upper Miocene to middle Pliocene. The submarine ridges were growing during Pilocene time. The Foxen mudstone is missing on them and in the northeastern part of the district. On the north limb of the Santa Maria Valley syncline, the Foxen overlaps the Sisquoc formation and rests on the basement. In the basins between the submarine ridges, the mudstone, siltstone, and fine-grained sandstone of the Foxen (800 feet thick in outcrop sections and as much as 2, 750 in subsurface sections) overlie conformably the Sisquoc formation. In some of the areas where the Foxen is missing as a lithologic unit, it appears to be represented by condensed deposits of phosphatic pellets, mapped with the underlying or overlying Formation, depending on the matrix, or by a condensed section of fine-grained sand, mapped with lithologically indistinguishable sand in the basal part of the overlying formation. Though foraminifera are abundant in the Foxen mudstone, relatively few species are represented. Those from the lower part of the formation may be of middle Pliocene age. Megafossils from the upper part of the Foxen are considered late Pliocene. The formation is therefore assigned to the middle(?) and upper Pliocene. Movements during Pliocene time in the basement area west of Point Sal Ridge are indicated by the occurrence in the western Casmalia Hills of coarse detritus from the Monterey in the upper part of the Sisquoc formation and in the Foxen mudstone. During late Pliocene time, when the Careaga sandstone was deposited, the Pliocene sea had its greatest extent. The region then flooded may be referred to as the Santa Maria basin. Throughout most of the district two mapped members of the Careaga sandstone are differentiated: the Cebada fine-grained member, which has a maximum outcrop thickness of 1,000 feet, and the Graciosa coarse-grained member, 50 to 425 feet thick. Mild deformation continued during the late Pliocene. The Cebada fine-grained member is missing on the embryonic anticlines, where it is overlapped by the Graciosa coarse-grained member. Both members of the Careaga sandstone contain a large megafauna. The nonmarine Paso Robles formation conformably overlies the Careaga sandstone. The Paso Robles consists chiefly of sand and gravel, but clay, marl, and limestone are the most characteristic constituents. The maximum outcrop thickness is 2,000 feet, the estimated maximum subsurface thickness 4,500 feet. The Paso Robles fresh-water fauna is meager, consisting of a few species similar to living forms. The formation is currently assigned to the interval including late Pliocene and early Pleistocene(?). The age assignment late Pliocene(?) and early Pleistocene, however, may be preferable for the Santa Maria district. Then followed the only period of strong general deformation in the known Tertiary and Pleistocene history of the district. The present structural features of the district were formed at that time, and the submarine ridges appeared as fully formed anticlines. Dating of the deformation is uncertain, because of uncertainty concerning the age of the Paso Robles formation. It is, however, without much doubt of the same age as the welldated strong middle Pleistocene deformation in the Ventura basin. Terrace deposits, laid down on both wave-cut and stream-cut platforms, are rather arbitrarily assigned to the late Pleistocene. The oldest and most extensive terrace deposits, not more than 100 feet thick, are designated the Orcutt sand. The Orcutt sand itself is tilted as much as 12° on the limbs of anticlines and is faulted on the north limb of the Graciosa anticline, indicating renewed growth of the anticlines, presumably in late Pleistocene time. Terrace deposits apparently younger than the Orcutt sand are arched in a low anticline west of lower Foxen Canyon. Structure.-Santa Maria Valley is the boundary between two structural provinces. To the north, valleys and hills are either synclines or anticlines. To the south, on the contrary, major valleys coincide generally with major synclines, and the hills are anticlinal. Santa Maria Valley itself is a syncline. Unlike valleys farther south in the district, however, it lies athwart an older uplift. Also unlike most of the valleys farther south, the axis of the syncline is not in the middle of the valley, but is far to the south near the bordering hills. Indeed, in the western Casmalia Hills, the anticline in the bordering hills is overturned and overrides the axis of the syncline. The major structural features of the district have a general west-northwestward trend parallel to the trend of the basin. Minor westward-trending and northward-trending folds and faults, however, extend across the trend of the major features. The district includes areas of wide, open folds and also areas of narrow, closely spaced, and steeply tilted folds, as well as some major overturned anticlines, most of the latter overturned northward. The closely spaced folds coincide almost invariably with outcrops of the Monterey shale and Point Sal formation. Physiography.-The surface on which the terrace deposits, designated the Orcutt sand, were deposited is extensive but is locally deformed, and only remnants are preserved. Toward the coast it changes from a stream-cut surface to a wave-cut surface. In the coastal area three main marine terraces are recognized: the high terrace (altitude about 800 feet), the intermediate terrace (altitude about 600 feet), and the low terrace (altitude 50 to 125 feet). An indurated layer is present at or near the surface at many localities scattered throughout the district. It is suggested that the indurated layer is an ancient hardpan, the incomplete skeleton of a former soil profile developed on a former surface of less relief than the present surface. Sand dunes extend inland from the coast at the north and south borders of the mapped area. They are classified under three age groups: old, intermediate, and modern. The old dunes, which have a protective cover of natural vegetation and are now inactive, are far more extensive than those of the other two groups. They cover many square miles on a terrace bordering Santa Maria Valley, and extend 20 miles inland. It has not been determined whether their inactivity is due to a cutting off of the supply of sand, or to a climatic change. Occurrence of oil.--Oil has been produced in the Santa Maria district since 1901, the total production to the end of 1947 being 269,657,000 barrels. Throughout the district most of the oil is heavy. Seven producing fields are located in the mapped area. In order of discovery from oldest to youngest the fields are as follows: Orcutt, Lompoc, West Cat Canyon, East Cat Canyon, Casmalia, Gato Ridge, and Santa Maria Valley. The Santa Maria Valley field is the largest in both area and productive capacity. It is the largest overlap field in coastal California, and one of the last major fields found in the State up to 1947. The Las Flores (Monterey) pool is transforming the West Cat Canyon field into one of the major fields of the district. The Monterey shale is the chief oil-bearing formation, and the principal reservoir in the Monterey consists of fractured chert and cherty shale. Sand in the Sisquoc formation is the sole reservoir in the minor East Cat Canyon field and in the Pliocene pool of the West Cat Canyon field. The Point Sal formation yields some oil in the southeastern part of the Santa Maria Valley field (the only part of that field where the formation is present) and a recent well in the Casmalia field is producing a small amount of relatively light oil from the Point Sal. The Lospe formation is also productive in a recent well in the Casmalia field. The Knoxville formation is productive in three areas in the northern part of the Santa Maria Valley field. The Point Sal formation offers the greatest promise for deeper-zone production. The Lospe and Knoxville formations can no longer be ignored in areas where younger marine formations overlap against them. Oil possibilities in undeveloped areas.--Two matters weigh heavily in prospecting in the Santa Maria district: the degree of fracturing of chert and cherty shale in the Monterey shale, and the gravity of the oil. Other things being equal, the productivity of the Monterey varies directly with the amount of fracturing. Very heavy oil, too heavy to produce commercially under present conditions, has befln found ii the Monterey in the northeastern part of the district, where five discoveries (one east of the mapped area) have been made in recent years. Among areas of possible interest, three appear to be favorable for prospecting on the basis of surface geology: an area east of Foxen Canyon, where oil may be trapped in the basal part of the Tinaquaic sandstone member of the Sisquoc formation by westward overlap of successively higher Tinaquaic strata onto the Monterey shale; an area so1tth of the I ... ions Head fault, where oil may be trapped by the fault; and the offshore extension of the north border of Point Sal Ridge, where oil may possibly be trapped in the Monterey by overlap of the Sisquoc formation.

California↗
USGS1969

Recent surface movements in the Baldwin Hills, Los Angeles County, California

The Baldwin Hills are located in the northwest part of the densely populated Los Angeles basin. They comprise one of several groups of isolated hills that extend along the northwest-trending Newport-Inglewood zone of folds and faults, a structural lineament identified with a series of very productive oil fields. In addition to being the site of the Inglewood oil field, these hills are the site of surface deformation that has been monitored for over 35 years. This record of deformation, which includes differential subsidence, horizontal displacements, and surface rupturing, forms one of the best documented examples of oilfield-associated surface deformation yet recognized. The deformation is described in detail, analyzed as to cause(s), and finally attributed largely or essentially entirely to the exploitation of the spatially-associated Inglewood oil field. The Baldwin Hills are underlain by gently to moderately arched and conspicuously faulted Cenozoic sedimentary and volcanic rocks that overlie crystalline basement rocks at a depth of more than 10,000 feet. The Inglewood fault, a part of the northwest-trending Newport-Inglewood zone, diagonally transects the hills. Right-lateral displacements of 3,000-4,000 feet since middle or late Pliocene time and 1,500-2,000 feet during Quaternary time are indicated by offset structural and physio-graphic features; indications of vertical separations of up to about 200 feet during late Quaternary time occur locally. Evidence of continuing deformation includes recognized seismicity and regional elevation changes. The M5-5 1/2 Inglewood earthquake of 1920, the largest local earthquake of record, is believed to have originated immediately southeast of the Baldwin Hills; it was apparently unassociated with surficial fault displacements. Leveling in and around the west and central Los Angeles basin has shown that lowland stations have been consistently subsiding, whereas foothill stations commonly have been rising. Several seemingly persistent basins of differential subsidence and a zone of positive movement, roughly coincident with the Newport-Inglewood zone, have also been identified in the northwest part of the basin. A prominent, elliptically-shaped, northwest-trending subsidence bowl encompassing the northwest part of the Baldwin Hills, has been defined by repeated level circuits. Partial reconstruction of selected level circuits with respect to a common, relatively stable control point (Hollywood E-11), located on the edge of the subsidence bowl, has permitted evaluation of the subsidence since 1910 and 1911 at two points near the center of the bowl. Thus bench mark PBM 67 is estimated to have subsided approximately 4.324 feet between June 1910 and February 1963; and bench mark PBM 68 (the only bench mark within the subsidence bowl that was leveled prior to 1926 and has been repeatedly leveled since) subsided 3.846 feet between November 1911 and June 1962. Analysis of the available data indicates little if any elevation change at PBM 68 (or elsewhere throughout the Baldwin Hills-Inglewood area) associated with the Inglewood earthquake of 1920. Maximum subsidence of PBM 122 (which has remained very close to the center of subsidence since at . least 1950) between 1911 and 1963 is calculated to have been 5.67 feet. Horizontal displacements (with respect to a north-south base line about 3 miles east of the hills) of six triangulation points within the subsidence bowl have been measured for various periods between 1934 and 1963. Displacements have been generally toward the center of subsidence and almost precisely perpendicular to the immediately adjacent isobases of equal elevation change. Maximum movement has been recorded at triangulation point Baldwin Aux, which was displaced 2.21 feet between 1934 and 1961; horizontal displacements of three additional points ranged from 0.95 foot to 1.85 feet between 1936 and 1961. Displacements of 0.10-0.29 foot were recorded at all six monuments during the period 1961-1963. "Earth cracks" and surficial fault displacements were recognized in the Baldwin Hills at least as early as 1957. The cracks are relatively straight, generally continuous fractures confined to the structural block east of the Inglewood fault; they are concentrated in two areas centering on (1) the Baldwin Hills Reservoir and (2) the Stocker Street-LaBrea Avenue-Overhill Drive intersection. The cracks trend north to north-northeast and are nearly everywhere parallel to or coincident with minor faults and joints, and are generally orthogonal to radii emanating from the center of subsidence. Differential movement along the cracks has been almost entirely dip slip along steep to nearly vertical surfaces, and generally down-dropped toward the center of subsidence. Cumulative displacements have been as much as 6 or 7 inches. Rates of displacement have ranged widely, and the movement has generally occurred as creep or very small discrete jumps. A probable exception is the several inches of differential movement that is believed to have occurred along a crack through the floor of the Baldwin Hills Reservoir on or about December 14, 1963. The contemporary surface movements are attributable to one or more of the following phenomena: (1). exploitation of the Inglewood oil field; (2) changes in the ground-water regimen; (3) compaction of sedimentary materials in response to surface loading; (4) tectonic activity. The following considerations indicate that the differential subsidence is attributable largely or entirely to exploitation of the underlying Inglewood oil field: (1) the coincidence of the centers of the oil field, the producing structure, and the subsidence bowl; (2) the general correspondence between the pattern of subsidence and the outlines of the oil field; (3) the approximate coincidence between the initiation of production and the initiation of subsidence; (4) the generally linear relations between various measures of subsidence and liquid production from both the field as a whole and the exceptionally prolific Vickers zone in particular; (5) the sharp deceleration of subsidence in the eastern block of the field coincident with the initiation of full-scale water flooding there; (6) the many examples of oil fields In which both spatial and temporal associations between production and subsidence are recognized; (7) the many similarities of the subsidence-production relations in the Inglewood field to those in the Wilmington field, where the subsidence has been authoritatively attributed to oilfield operations; (8) the theoretical relation between subsidence or a tendency toward subsidence and increased effective pressure associated with underground fluid extraction. Consideration of six possible explanations for the increasing rather than decreasing or constant rate of subsidence with respect to reservoir fluid pressure decline suggests that measured or calculated down-hole reservoir fluid pressure decline is non-representative of average or real fluid pressure decline away from producing wells. The near-linear relations between net-liquid production and subsidence are explained through analogy with a tightly confined artesian system of infinite areal extent, where production must derive from liquid expansion and/or reservoir compaction. Test data from compaction studies in two other oil fields yield estimates of ultimate compaction of the Vickers zone resulting from a total loss of fluid pressure; these estimates range over an order of magnitude. The best estimate, based on these data and considerations of late Cenozoic history in the Baldwin Hills area, is about 10 feet. The centripetally-directed horizontal movements are considered attributable to exploitation of the Inglewood oil field on the basis of: (1) their well-defined symmetrical and geometrical association with the differential subsidence; (2) the similarities between these associations and those developed in and around other subsiding oil fields; and (3) the mechanical compatibility of these movements with subsidence induced by the extraction of subsurface materials. The earth cracks and surficial fault displacements are considered largely or entirely attributable to the exploitation of the Inglewood oil field on the basis of: (1) their spatial and temporal relations to both oil-field operations and the differential subsidence; (2) the similarities of these cracks and displacements to those generated in and around other oil fields and areas of subsurface materials extraction; and (3) surface strain patterns predicted from the measured vertical and horizontal surface movements. The cracks and displacements can i)e explained by an exploitation-based, elastic-rebound model which requires elastic compression of the sedimentary section in response to compaction-induced downdrag within those blocks around the periphery of the subsidence bowl. The measured displacements have been about one-quarter to one-half those predicted for a purely elastic system. Analysis of: (1) the history of ground-water extraction within and around the Baldwin Hills; and (2) subsidence associated with water-level declines in sediments comparable with those in the Baldwin Hills, indicate that the surface movements can be no more than incidentally attributed to changes in ground-water conditions. Similarly, analysis of the history of natural and artificial changes in surface loading indicate that these movements are generally unassociated with changes in surface loading conditions. Considerations of local geologic history and various tectonic associations indicate that it is very unlikely that the differential subsidence and horizontal movements are due to tectonic downwarping. There exists a far stronger prima facie argument for tectonic involvement in the earth cracking and associated fault displacements. This argument is disputed by; (1) the spatial and temporal relations of the earth cracks to, and their mechanical compatibility with, the nontectonic differential subsidence; (2) the absence of displacements on the Inglewood fault in conjunction with those along the conjugate earth cracks; (3) the probability that purely tectonic displaceMents would be characterized by oblique or strike slip; and (4) the absence of any clear temporal relation between crack growth and local seismicity, However, because as much as 10 percent of the local isobase gradient may be unexplained' by oil-field exploitation, a small fraction of this gradient, and thus the displacements among the southern group of cracks, may be attributable to tectonic activity. This fraction should have been insignificant in the presence of the strain pattern produced by nontectonic compaction of the underlying oil measures. Because nearly all of the observed and measured surface movements can be fully explained as the products of oil-field operations, yet can be no more than incidentally attributed to changes in ground-water conditions, surface loading, or tectonic activity, we conclude that these movements are attributable largely or essentially entirely to the exploitation of the Inglewood oil field.

California↗