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Research about Riverside County, California

Source-linked reports with geographic coverage including Riverside County, California.

At least 19 recordsLinked to original sources
USGS2021

Landscape evolution in eastern Chuckwalla Valley, Riverside County, California

This study investigates sedimentary and geomorphic processes in eastern Chuckwalla Valley, Riverside County, California, a region of arid, basin-and-range terrain where extensive solar-energy development is planned. The objectives of this study were to (1) measure local weather parameters and use them to model aeolian sediment-transport potential; (2) identify surface sedimentary characteristics in representative localities; and (3) evaluate long-term landscape evolution rates and processes by analyzing stratigraphy in combination with luminescence geochronology. The new stratigraphic and geochronologic data presented in this report demonstrate the varying local significance of aeolian, alluvial fan, lacustrine (playa), and possibly Colorado River influence over a range of time scales. The dominant sand-transport direction in eastern Chuckwalla Valley is toward the northeast, consistent with the recognized regional west-to-east wind direction. However, occasional strong wind events from the north can transport large quantities of sand southward and temporarily reshape local geomorphic features. Influence of a northwest wind direction is also locally dominant around mountain ranges and controls the modern morphology of the Palen dune field. Modeled sand fluxes are on the order of 10 5 kilograms per meter width per year at the site of weather monitoring, 5 kilometers northwest of the Mule Mountains. Aeolian dunes are locally well developed and actively migrating. Their location and activity are determined largely by sediment supply from playa surfaces and ephemeral stream channels, which also control the dunes’ spatial extent and migration potential; stream channels act as both source and sink for aeolian sediment in this environment. Excavations at five sites along a northwest-to-southeast transect reveal that playa deposits formed around 266–226 thousand years ago south of the McCoy Mountains and immediately north of the present location of Interstate 10. The playa material is overlain by late Pleistocene to Holocene alluvial fan deposits. To the southeast (south of Interstate 10, but north of the Mule Mountains), we identified rapid accumulation of alluvial sediment around the time of the Last Glacial Maximum (23–20 thousand years ago), unconformably overlain by a locally varying assemblage of recent aeolian material or Holocene alluvial fan sediment. We have used stratigraphic characteristics and luminescence ages to calculate accumulation rates for sites in eastern Chuckwalla Valley, and thereby to identify spatial variation in landscape stability over decadal and longer time scales. If future solar-energy development plans are to include natural sand-transport corridors, plans would entail retaining the ability for sand to be transported eastward from the ephemeral stream channels and playas that supply sediment to the dunes, sand sheets, and sand ramps of Chuckwalla Valley, and also to allow for southward transport during episodic strong weather events several times per year. The aeolian sediment-transport corridors are dynamic spatially and temporally, reorganizing on the basis of seasonal changes to wind drift potential. Future landscape stability also will be determined by climate-driven changes to vegetation and thereby to aeolian sediment availability. In a warmer, drier climate, aeolian sediment activity is expected to increase, owing to a decrease in stabilizing vegetation cover and more extreme rain that supplies sediment to ephemeral stream channels and playas from which it is remobilized by wind.

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USGS2020

Seismic evaluation of shallow-depth structure, faulting, and groundwater variations across the Dos Palmas Preserve, Riverside County, California

Introduction Dos Palmas Preserve is a Colorado Desert oasis and wetland in Riverside County, California, located near the base of the Orocopia Mountains and northeast of the Salton Sea. The original source of water for the oasis was artesian springs that developed at the base of the Orocopia Mountains, but more abundant water supplies were later provided to Dos Palmas Preserve when the Coachella Canal was built and water seeped from unlined parts of the canal. As a result of this abundant water supply in a desert setting, Dos Palmas Preserve, managed by the Bureau of Land Management, is now a wildlife preserve that became home to multiple plants, fowl, insects, rodents, reptiles, and bats, including some endangered and threatened species. More recently, sections of the Coachella Canal have been lined, resulting in a reduction of water seepage and threatening the sustainability of parts of Dos Palmas Preserve. Faults usually act as barriers to groundwater flow and Dos Palmas Preserve is only a few kilometers from the active trace of the San Andreas Fault, where splays of the fault trend through the area. Additionally, numerous closely spaced faults that have been mapped at the surface northwest of Dos Palmas Preserve are believed to extend southward into the Dos Palmas Preserve, where they are covered by alluvium. Thus, evaluation of the subsurface lithology and structure is needed to determine how the current allocation of water from the Coachella Canal affects various parts of Dos Palmas Preserve. To better understand the distribution of the shallow lithology, faulting, and groundwater in Dos Palmas Preserve, the U.S. Geological Survey, in collaboration with the Bureau of Land Management, conducted a seismic survey across the northern part of Dos Palmas Preserve. The seismic survey was designed to “map” the upper part of the aquifer system and to more precisely locate faults that may affect groundwater flow in Dos Palmas Preserve. In this report, we present seismic velocity and reflection images of the shallow subsurface and relate those images to interpretative structures and stratigraphy that may affect groundwater at Dos Palmas Preserve.

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USGS2015

Speocarcinus berglundi n. sp. (Decapoda: Brachyura), a new crab from the Imperial Formation (late Miocene-late Pliocene) of southern California

Speocarcinus berglundi n. sp. is described from the Imperial Formation in Riverside County, California. Although the Imperial Formation spans late Miocene through late Pliocene time, the part of the unit that bears crabs has been radiometrically dated as late Miocene. The identification of a new species was based upon comparison with four extant species and represents the first documented fossil occurrence for the genus. The occurrence of this new species suggests that the genus may have originated in the Pacific and, during the Miocene, dispersed through the Isthmus of Panama to the Caribbean. Two of the specimens exhibit parasitism by Bopyridae (Isopoda).

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USGS2015

Using motion-sensor camera technology to infer seasonal activity and thermal niche of the desert tortoise ( Gopherus agassizii )

Understanding the relationships between environmental variables and wildlife activity is an important part of effective management. The desert tortoise ( Gopherus agassizii ), an imperiled species of arid environments in the southwest US, may have increasingly restricted windows for activity due to current warming trends. In summer 2013, we deployed 48 motion sensor cameras at the entrances of tortoise burrows to investigate the effects of temperature, sex, and day of the year on the activity of desert tortoises. Using generalized estimating equations, we found that the relative probability of activity was associated with temperature (linear and quadratic), sex, and day of the year. Sex effects showed that male tortoises are generally more active than female tortoises. Temperature had a quadratic effect, indicating that tortoise activity was heightened at a range of temperatures. In addition, we found significant support for interactions between sex and day of the year, and sex and temperature as predictors of the probability of activity. Using our models, we were able to estimate air temperatures and times (days and hours) that were associated with maximum activity during the study. Because tortoise activity is constrained by environmental conditions such as temperature, it is increasingly vital to conduct studies on how tortoises vary their activity throughout the Sonoran Desert to better understand the effects of a changing climate.

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USGS2015

Geologic and geophysical maps of the El Casco 7.5′ quadrangle, Riverside County, southern California, with accompanying geologic-map database

Introduction Earth materials and structures in the El Casco quadrangle provide considerable information about the late Cenozoic geologic evolution of southern California’s Inland Empire region (fig. 2). Important structural and stratigraphic elements include (1) modern traces of the right-lateral San Jacinto Fault zone, (2) older traces of the San Jacinto Fault zone, and (3) sedimentary materials and geologic structures that formed during the last eight million years or so and that record interactions within the San Andreas Fault system. These materials, and the structures that deform them, provide a geologic context 3 for investigations of groundwater recharge and subsurface flow (Waring, 1919; Burnham and Dutcher, 1960; Bloyd, 1971; Rewis and others, 2006). This geologic database of the El Casco 7.5′ quadrangle was prepared by the Basins and Landscape Co-Evolution Project (BALANCE), a regional geologic-mapping project sponsored jointly by the U.S. Geological Survey and the California Geological Survey. The database was developed as a contribution to the National Cooperative Geologic Mapping Program’s National Geologic Map Database, and provides a general geologic setting of the El Casco quadrangle. The database and map provide information about earth materials and geologic structures, including faults and folds that have developed in the quadrangle due to complexities in the San Andreas Fault system. Geologic information contained in the El Casco database is general-purpose data applicable to land-related investigations in the earth and biological sciences. The term “general-purpose” means that all geologic-feature classes have minimal information content adequate to characterize their general geologic characteristics and to interpret their general geologic history. However, no single feature class has enough information to definitively characterize its properties and origin. For this reason the database cannot be used for site-specific geologic evaluations, although it can be used to plan and guide investigations at the site-specific level.

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USGS2014

Petrology and chemistry of the Green Acres gabbro complex near Winchester, Riverside County, California

The Cretaceous Green Acres layered igneous complex, northeast of Winchester, California, is composed of a suite of olivine- and hornblende-bearing gabbros in the Peninsular Ranges batholith within the Perris tectonic block. A consistent mineral assemblage is observed throughout the complex, but there is considerable textural and modal heterogeneity. Both preclude a consistent set of principles based on appearance and mineralogy on which to delineate map units. Distinct changes in the chemistry of olivine, pyroxene, and hornblende, however, serve to define discrete mappable units, and the complex has been divided into five geochemical map units on this basis. Limited whole-rock data show the Green Acres complex is chemically comparable to other Peninsular Ranges batholith gabbroic rocks, and rare earth element (REE) concentrations and patterns are typical of magmas generated in convergent margin settings. For the complex as a whole, olivine is Fo 80–35 , plagioclase is An 100–64 , clinopyroxene is Wo 49–41 En 48–38 Fs 18–6 and Wo 36–26 En 65–42 Fs 30–8 , and orthopyroxene is Wo 5–0 En 78–42 Fs 50–21 , where Fo is forsterite, An is anorthite, Wo is wollastonite, En is enstatite, and Fs is ferrosilite. The Mg/(Mg + ΣFe) atomic ratio in hornblende ranges from 0.84 to 0.50. Magmatic lineations and modal and textural layering are prevalent throughout the complex. Mineral chemistry does not change in any systematic way within and between layers in any map unit. Although the strike of layering varies, in any map unit at any given location it is the same in all units irrespective of intrusive order. Thin dikes, typically late-stage hornblende gabbro, commonly intrude parallel to layering. The strikes of magmatic lineations and modal layers are consistent with the populations of strikes of fabrics in the metamorphic basement as well as tectonic features in surrounding, postgabbro granitic rocks. These relations imply that the regional state of stress at the time of gabbro emplacement played a role in layer formation in conjunction with thermal and hydraulic pressure perturbations.

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USGS2005

Preliminary geologic map of the Hemet 7.5' quadrangle, Riverside County, California

The Hemet 7.5' quadrangle is located near the eastern edge of the Perris block of the Peninsular Ranges batholith. The northeastern corner of the quadrangle extends across the San Jacinto Fault Zone onto the edge of the San Jacinto Mountains block. The Perris block is a relatively stable area located between the Elsinore Fault Zone on the west and the San Jacinto Fault Zone on the east. Both of the fault zones are active; the San Jacinto being the seismically most active in southern California. The fault zone is obscured by very young alluvial deposits. The concealed location of the San Jacinto Fault Zone shown on this quadrangle is after Sharp, 1967. The geology of the quadrangle is dominated by Cretaceous tonalite formerly included in the Coahuila Valley pluton of Sharp (1967). The northern part of Sharp's Coahuila Valley pluton is separated out as the Hemet pluton. Tonalite of the Hemet pluton is more heterogeneous than the tonalite of the Coahuila Valley pluton and has a different sturctural pattern. The Coahuila Valley pluton consists of relatively homogeneous hornblende-biotite tonalite, commonly with readily visible large euhedral honey-colored sphene crystals. Only the tip of the adjacent Tucalota Valley pluton, another large tonalite pluton, extends into the quadrangle. Tonalite of the Tucalota Valley pluton is very similar to the tonalite of the Coahuila Valley pluton except it generally lacks readily visible sphene. In the western part of the quadrangle a variety of amphibolite grade metasedimentary rocks are informally referred to as the rocks of Menifee Valley; named for exposures around Menifee Valley west of the Hemet quadrangle. In the southwestern corner of the quadrangle a mixture of schist and gneiss marks a suture that separated low metamorphic grade metasedimentary rocks to the west from high metamorphic grade rocks to the east. The age of these rocks is interpreted to be Triassic and the age of the suturing is about 100 Ma, essentially the same age as the adjacent Coahuila Valley pluton. Rocks within the suture zone consist of a mixture of lithologies from both sides of the suture. Gneiss, schist, and anatectic gneiss are the predominate lithologies within the rocks on the east side of the suture. Lesser amounts of metalithic greywacke and lenticular masses of black amphibolite are subordinate rock types. Biotite, biotite-sillimanite and lesser amounts of garnet-biotite-sillimanite schist and metaquartzite-metalithic greywacke lithologies occur west of the suture. Pleistocene continental beds, termed the Bautista beds occur east of the San Jacinto Fault Zone in the northeast corner of the quadrangle. Most of the Bautista beds were derived from the San Jacinto pluton that is located just to the east of the sedimentary rocks. Along the northern part of the quadrangle is the southern part of a large Holocene-late Pleistocene fan emanating from Baustista Canyon. Sediments in the Bautista fan are characterized by their content of detritus derived from amphibolite grade metasedimentary rocks located in the Bautista Canyon drainage. Between the Holocene-late Pleistocene Bautista fan and the Santa Rosa Hills is the remnant of a much older Bautista Canyon alluvial fan. A pronounced Holocene-late Pleistocene channel was developed along the south fringe of the very old alluvial fan and the Santa Rosa Hill. A now dissected late to middle Pleistocene alluvial complex was produced by the coalesced fans of Goodhart, St. Johns, and Avery canyons, and Cactus Valley. Pleistocene continental beds, termed the Bautista beds occur east of the San Jacinto Fault Zone in the northeast corner of the quadrangle. Most of the Bautista beds were derived from the San Jacinto pluton that is located just to the east of the sedimentary rocks. Along the northern part of the quadrangle is the southern part of a large Holocene-late Pleistocene fan emanating from Baustista Canyon.

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USGS2003

Geologic map and digital database of the Romoland 7.5' quadrangle, Riverside County, California

Open-File Report 03-102 contains a digital geologic map database of the Romoland 7.5’ quadrangle, Riverside County, California that includes: ARC/INFO (Environmental Systems Research Institute, http://www.esri.com) version 7.2.1 coverages of the various elements of the geologic map. A Postscript file to plot the geologic map on a topographic base, and containing a Correlation of Map Units diagram (CMU), a Description of Map Units (DMU), and an index map. Portable Document Format (.pdf) files of: This Readme; includes in Appendix I, data contained in rom_met.txt The same graphic as plotted in 2 above. Test plots have not produced precise 1:24,000- scale map sheets. Adobe Acrobat page size setting influences map scale. The Correlation of Map Units and Description of Map Units is in the editorial format of USGS Geologic Investigations Series (I-series) maps but has not been edited to comply with I-map standards. Within the geologic map data package, map units are identified by standard geologic map criteria such as formationname, age, and lithology. Where known, grain size is indicated on the map by a subscripted letter or letters following the unit symbols as follows: lg, large boulders; b, boulder; g, gravel; a, arenaceous; s, silt; c, clay; e.g. Qyfa is a predominantly young alluvial fan deposit that is arenaceous. Multiple letters are used for more specific identification or for mixed units, e.g., Qfysa is a silty sand. In some cases, mixed units are indicated by a compound symbol; e.g., Qyf2sc. Even though this is an Open-File Report and includes the standard USGS Open-File disclaimer, the report closely adheres to the stratigraphic nomenclature of the U.S. Geological Survey. Descriptions of units can be obtained by viewing or plotting the .pdf file (3b above) or plotting the postscript file (2 above). This Readme file describes the digital data, such as types and general contents of files making up the database, and includes information on how to extract and plot the map and accompanying graphic file. Metadata information can be accessed at http://geo-nsdi.er.usgs.gov/metadata/open-file/03-102 and is included in Appendix I of this Readme.

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USGS2003

Geologic map and digital database of the Bachelor Mountain 7.5' quadrangle, Riverside County, California

Open-File Report 03-102 contains a digital geologic map database of the Bachelor Mountain 7.5’ quadrangle, Riverside County, California that includes: ARC/INFO (Environmental Systems Research Institute, http://www.esri.com) version 7.2.1 coverages of the various elements of the geologic map. A Postscript file to plot the geologic map on a topographic base, and containing a Correlation of Map Units diagram (CMU), a Description of Map Units (DMU), and an index map. Portable Document Format (.pdf) files of: This Readme; includes in Appendix I, data contained in bch_met.txt The same graphic as plotted in 2 above. Test plots have not produced precise 1:24,000- scale map sheets. Adobe Acrobat page size setting influences map scale. The Correlation of Map Units and Description of Map Units is in the editorial format of USGS Geologic Investigations Series (I-series) maps but has not been edited to comply with I-map standards. Within the geologic map data package, map units are identified by standard geologic map criteria such as formationname, age, and lithology. Where known, grain size is indicated on the map by a subscripted letter or letters following the unit symbols as follows: lg, large boulders; b, boulder; g, gravel; a, arenaceous; s, silt; c, clay; e.g. Qyfa is a predominantly young alluvial fan deposit that is arenaceous. Multiple letters are used for more specific identification or for mixed units, e.g., Qfysa is a silty sand. In some cases, mixed units are indicated by a compound symbol; e.g., Qyf2sc. Even though this is an Open-File Report and includes the standard USGS Open-File disclaimer, the report closely adheres to the stratigraphic nomenclature of the U.S. Geological Survey. Descriptions of units can be obtained by viewing or plotting the .pdf file (3b above) or plotting the postscript file (2 above). This Readme file describes the digital data, such as types and general contents of files making up the database, and includes information on how to extract and plot the map and accompanying graphic file. Metadata information can be accessed at http://geo-nsdi.er.usgs.gov/metadata/open-file/03-102 and is included in Appendix I of this Readme.

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USGS2003

Preliminary geologic map of the Murrieta 7.5' quadrangle, Riverside County, California

The Murrieta quadrangle is located in the northern part of the Peninsular Ranges Province and includes parts of two structural blocks, or structural subdivisions of the province. The quadrangle is diagonally crossed by the active Elsinore fault zone, a major fault zone of the San Andreas fault system, and separates the Santa Ana Mountains block to the west from the Perris block to the east. Both blocks are relatively stable internally and within the quadrangle are characterized by the presence of widespread erosional surfaces of low relief. The Santa Ana Mountains block, in the Murrieta quadrangle, is underlain by undifferentiated, thick-layered, granular, impure quartzite and well-layered, fissile, phyllitic metamorphic rock of low metamorphic grade. Both quartzite and phyllitic rocks are Mesozoic. Unconformably overlying the metamorphic rocks are remnants of basalt flows having relatively unmodified flow surfaces. The age of the basalt is about 7-8Ma. Large shallow depressions on the surface of the larger basalt remnants form vernal ponds that contain an endemic flora. Beneath the basalt the upper part of the metamorphic rocks is deeply weathered. The weathering appears to be the same as the regional Paleocene saprolitic weathering in southern California. West of the quadrangle a variable thickness sedimentary rock, physically resembling Paleogene rocks, occurs between the basalt and metamorphic rock. Where not protected by the basalt, the weathered rock has been removed by erosion. The dominant feature on the Perris block in the Murrieta quadrangle is the south half of the Paloma Valley ring complex, part of the composite Peninsular Ranges batholith. The complex is elliptical in plan view and consists of an older ring-dike with two subsidiary short-arced dikes that were emplaced into gabbro by magmatic stoping. Small to large stoped blocks of gabbro are common within the ring-dikes. A younger ring-set of hundreds of thin pegmatite dikes occur largely within the central part of the complex. These pegmatite dikes were emplaced into a domal fracture system, apparently produced by cauldron subsidence, and include in the center of the complex, a number of flat-floored granophyre bodies. The granophyre is interpreted to be the result of pressure quenching of pegmatite magma. Along the eastern edge of the quadrangle is the western part of a large septum of medium metamorphic grade Mesozoic schist. A dissected basalt flow caps the Hogbacks northeast of Temecula, and represents remnants of a channel filling flow. Beneath the basalt is a thin deposit of stream gravel. Having an age of about 10Ma, this basalt is about 2-3Ma older than the basalt flows in the Santa Ana Mountains. The Elsinore fault zone forms a complex of pull-apart basins. The west edge of the fault zone, the Willard Fault, is marked by the high, steep eastern face of the Santa Ana Mountains. The east side of the zone, the Wildomar Fault, forms a less pronounced physiographic step. In the center of the quadrangle a major splay of the fault zone, the Murrieta Hot Springs Fault, strikes east. Branching of the fault zone causes the development of a broad alluvial valley between the Willard Fault and the Murrieta Hot Springs Fault. All but the axial part of the zone between the Willard and Wildomar Faults consist of dissected Pleistocene sedimentary units. The axial part of the zone is underlain by Holocene and latest Pleistocene sedimentary units.

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USGS2003

Preliminary geologic map of the Perris 7.5' quadrangle, Riverside County, California

Open-File Report 03-270 contains a digital geologic map database of the Perris 7.5’ quadrangle, Riverside County, California that includes: 1. ARC/INFO (Environmental Systems Research Institute, http://www.esri.com) version 7.2.1 coverages of the various elements of the geologic map. 2. A Postscript file to plot the geologic map on a topographic base, and containing a Correlation of Map Units diagram (CMU), a Description of Map Units (DMU), and an index map. 3. Portable Document Format (.pdf) files of: a. A Readme file b. The same graphic as described in 2 above. Test plots have not produced precise 1:24,000- scale map sheets. Adobe Acrobat page size setting influences map scale. The Correlation of Map Units and Description of Map Units is in the editorial format of USGS Geologic Investigations Series (I-series) maps but has not been edited to comply with I-map standards. Within the geologic map data package, map units are identified by standard geologic map criteria such as formationname, age, and lithology. Where known, grain size is indicated on the map by a subscripted letter or letters following the unit symbols as follows: lg, large boulders; b, boulder; g, gravel; a, arenaceous; s, silt; c, clay; e.g. Qyfa is a predominantly young alluvial fan deposit that is arenaceous. Multiple letters are used for more specific identification or for mixed units, e.g., Qfysa is a silty sand. In some cases, mixed units are indicated by a compound symbol; e.g., Qyf2sc.

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USGS2003

Preliminary geologic map of the Elsinore 7.5' quadrangle, Riverside County, California

Open-File Report 03-281 contains a digital geologic map database of the Elsinore 7.5’ quadrangle, Riverside County, California that includes: 1. ARC/INFO (Environmental Systems Research Institute, http://www.esri.com) version 7.2.1 coverages of the various elements of the geologic map. 2. A Postscript file to plot the geologic map on a topographic base, and containing a Correlation of Map Units diagram (CMU), a Description of Map Units (DMU), and an index map. 3. Portable Document Format (.pdf) files of: a. This Readme; includes in Appendix I, data contained in els_met.txt b. The same graphic as plotted in 2 above. Test plots have not produced precise 1:24,000-scale map sheets. Adobe Acrobat page size setting influences map scale. The Correlation of Map Units and Description of Map Units is in the editorial format of USGS Geologic Investigations Series (I-series) maps but has not been edited to comply with I-map standards. Within the geologic map data package, map units are identified by standard geologic map criteria such as formation-name, age, and lithology. Where known, grain size is indicated on the map by a subscripted letter or letters following the unit symbols as follows: lg, large boulders; b, boulder; g, gravel; a, arenaceous; s, silt; c, clay; e.g. Qyfa is a predominantly young alluvial fan deposit that is arenaceous. Multiple letters are used for more specific identification or for mixed units, e.g., Qfysa is a silty sand. In some cases, mixed units are indicated by a compound symbol; e.g., Qyf2sc. Even though this is an Open-File Report and includes the standard USGS Open-File disclaimer, the report closely adheres to the stratigraphic nomenclature of the U.S. Geological Survey. Descriptions of units can be obtained by viewing or plotting the .pdf file (3b above) or plotting the postscript file (2 above).

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USGS2002

Geologic map and digital database of the Pinto Mountain 7.5 minute quadrangle, Riverside County, California

The geologic map and digital database of the Pinto Mountain quadrangle are products of a regional geologic mapping effort undertaken in the eastern Transverse Ranges in and around Joshua Tree National Park. This investigation, part of the Southern California Areal Mapping Project (SCAMP), is conducted in cooperation with the California Geologic Survey and the National Park Service. In line with the goals of the National Cooperative Geologic Mapping Program (NCGMP), mapping of the Pinto Mountain and other quadrangles has been directed toward generating a multipurpose digital geologic map database that is applicable to land-related investigations in the earth and biological sciences. This mapping is conducted to further understanding of bedrock geology and surficial processes in the region and to document evidence for seismotectonic activity in the eastern Transverse Ranges. It is also intended to serve as a base layer suitable for ecosystem and mineral resource assessment and for building a hydrogeologic framework for Pinto Basin. Initial investigations span Pinto Basin from the Hexie and Eagle Mountains northward into the Pinto Mountains. Quadrangles mapped include the Conejo Well 7.5-minute quadrangle (Powell, 2001a), the Porcupine Wash 7.5-minute quadrangle (Powell, 2001b), the Pinto Mountain 7.5-minute quadrangle, and the San Bernardino Wash 7.5-minute quadrangle (Powell, 2002). Parts of the Pinto Mountain quadrangle had been mapped previously at a variety of scales (Weir, and Bader, 1963; Hope, 1966, 1969; Jennings, 1967; Powell, 1981, 1993).

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USGS2002

Geologic map and digital database of the San Bernardino Wash 7.5 minute quadrangle, Riverside County, California

The geologic map and digital database of the San Bernardino Wash quadrangle are products of a regional geologic mapping effort undertaken in the eastern Transverse Ranges in and around Joshua Tree National Park. This investigation, part of the Southern California Areal Mapping Project (SCAMP), is conducted in cooperation with the California Geologic Survey and the National Park Service. In line with the goals of the National Cooperative Geologic Mapping Program (NCGMP), mapping of the San Bernardino Wash and other quadrangles has been directed toward generating a multipurpose digital geologic map database that is applicable to land-related investigations in the earth and biological sciences. This mapping is conducted to further understanding of bedrock geology and surficial processes in the region and to document evidence for seismotectonic activity in the eastern Transverse Ranges. It is also intended to serve as a base layer suitable for ecosystem and mineral resource assessment and for building a hydrogeologic framework for Pinto Basin. Initial investigations span Pinto Basin from the Hexie and Eagle Mountains northward into the Pinto Mountains (see fig. 1). Quadrangles mapped include the Conejo Well 7.5-minute quadrangle (Powell, 2001a), the Porcupine Wash 7.5-minute quadrangle (Powell, 2001b), the Pinto Mountain 7.5-minute quadrangle (Powell, 2002), and the San Bernardino Wash 7.5-minute quadrangle. Parts of the San Bernardino Wash quadrangle had been mapped previously at a variety of scales (Weir, and Bader, 1963; Hope, 1966, 1969; Jennings, 1967; Powell, 1981, 1993).

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USGS2002

Rainfall-runoff characteristics and effects of increased urban density on streamflow and infiltration in the eastern part of the San Jacinto River basin, Riverside County, California

To better understand the rainfall-runoff characteristics of the eastern part of the San Jacinto River Basin and to estimate the effects of increased urbanization on streamflow, channel infiltration, and land-surface infiltration, a long-term (1950?98) time series of monthly flows in and out of the channels and land surfaces were simulated using the Hydrologic Simulation Program- FORTRAN (HSPF) rainfall-runoff model. Channel and land-surface infiltration includes rainfall or runoff that infiltrates past the zone of evapotranspiration and may become ground-water recharge. The study area encompasses about 256 square miles of the San Jacinto River drainage basin in Riverside County, California. Daily streamflow (for periods with available data between 1950 and 1998), and daily rainfall and evaporation (1950?98) data; monthly reservoir storage data (1961?98); and estimated mean annual reservoir inflow data (for 1974 conditions) were used to calibrate the rainfall-runoff model. Measured and simulated mean annual streamflows for the San Jacinto River near San Jacinto streamflow-gaging station (North-South Fork subbasin) for 1950?91 and 1997?98 were 14,000 and 14,200 acre-feet, respectively, a difference of 1.4 percent. The standard error of the mean for measured and simulated annual streamflow in the North-South Fork subbasin was 3,520 and 3,160 acre-feet, respectively. Measured and simulated mean annual streamflows for the Bautista Creek streamflow-gaging station (Bautista Creek subbasin) for 1950?98 were 980 acre-feet and 991 acre-feet, respectively, a difference of 1.1 percent. The standard error of the mean for measured and simulated annual streamflow in the Bautista Creek subbasin was 299 and 217 acre-feet, respectively. Measured and simulated annual streamflows for the San Jacinto River above State Street near San Jacinto streamflow-gaging station (Poppet subbasin) for 1998 were 23,400 and 23,500 acre-feet, respectively, a difference of 0.4 percent. The simulated mean annual streamflow for the State Street gaging station at the outlet of the study basin and the simulated mean annual basin infiltration (combined infiltration from all the channels and land surfaces) were 8,720 and 41,600 acre-feet, respectively, for water years 1950-98. Simulated annual streamflow at the State Street gaging station ranged from 16.8 acre-feet in water year 1961 to 70,400 acre-feet in water year 1993, and simulated basin infiltration ranged from 2,770 acre-feet in water year 1961 to 149,000 acre-feet in water year 1983. The effects of increased urbanization on the hydrology of the study basin were evaluated by increasing the size of the effective impervious and non-effective impervious urban areas simulated in the calibrated rainfall-runoff model by 50 and 100 percent, respectively. The rainfall-runoff model simulated a long-term time series of monthly flows in and out of the channels and land surfaces using daily rainfall and potential evaporation data for water years 1950?98. Increasing the effective impervious and non-effective impervious urban areas by 100 percent resulted in a 5-percent increase in simulated mean annual streamflow at the State Street gaging station, and a 2.2-percent increase in simulated basin infiltration. Results of a frequency analysis of the simulated annual streamflow at the State Street gaging station showed that when effective impervious and non-effective impervious areas were increased 100 percent, simulated annual streamflow increased about 100 percent for low-flow conditions and was unchanged for high-flow conditions. The simulated increase in streamflow at the State Street gaging station potentially could infiltrate along the stream channel further downstream, outside of the model area.

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USGS2002

Detection and measurement of land subsidence using global positioning system and Interferometric Synthetic Aperture Radar, Coachella Valley, California, 1998-2000

Land subsidence associated with ground-water-level declines has been recognized as a potential problem in Coachella Valley, California. Since the early 1920s, ground water has been a major source of agricultural, municipal, and domestic supply in the valley. Pumping of ground water resulted in water-level declines as large as 15 meters (50 feet) through the late 1940s. In 1949, the importation of Colorado River water to the lower Coachella Valley began, resulting in a reduction in ground-water pumping and a recovery of water levels during the 1950s through the 1970s. Since the late 1970s, demand for water in the valley has exceeded deliveries of imported surface water, resulting in increased pumping and associated ground-water-level declines and, consequently, an increase in the potential for land subsidence caused by aquifer-system compaction. The location, extent, and magnitude of the vertical land-surface changes in Coachella Valley between 1998 and 2000 were determined using Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR) methods. GPS measurements made at 15 geodetic monuments in the lower Coachella Valley indicate that -34 to +60 millimeters ± 45 millimeters (-0.11 to +0.20 foot ± 0.15 foot) of vertical change in the land surface occurred during the 2-year period. Changes at three of the monuments exceeded the maximum uncertainty of ± 45 millimeters (± 0.15 foot) at the 95-percent confidence level, which indicates that small amounts of uplift occurred at these monuments between October 1998 and August 2000. Water-level measurements made at wells near the three uplifted monuments during this 2-year period indicate that the water levels fluctuate seasonally; water-level measurements made at these wells in September 1998 and September 2000 indicate that the water levels rose slightly near two monuments and declined slightly near the third. The relation between the seasonally fluctuating, but fairly stable, water levels between September 1998 and September 2000 and the slight uplift at the monuments may indicate that the water levels are fluctuating in the elastic range of stress and that the preconsolidation stress of the aquifer system was not exceeded during the 2-year period. Results of the InSAR measurements made between June 17, 1998, and October 4, 2000, indicate that land subsidence, ranging from about 40 to 80 millimeters (0.13 to 0.26 foot), occurred in three areas of the Coachella Valley; near Palm Desert, Indian Wells, and La Quinta. Measurements made between June 17, 1998, and June 2, 1999, indicate that about 15 millimeters (0.05 foot) occurred southeast of Lake Cahuilla. All the subsiding areas coincide with or are near areas where ground-water levels declined between 1998 and 2000; some water levels in 2000 were at the lowest levels in their recorded histories. The coincident areas of subsidence and declining water levels suggest that aquifer-system compaction may be causing subsidence. If the stresses imposed by the historically lowest water levels exceeded the preconsolidation stress, the aquifer-system compaction and associated land subsidence may be permanent. Although the localized character of the subsidence signals look typical of the type of subsidence characteristically caused by localized pumping, the subsidence also may be related to tectonic activity in the valley.

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USGS2001

Geologic map of the Lakeview 7.5' quadrangle, Riverside County, California

This Open-File Report contains a digital geologic map and map database of the Lakeview 7.5' quadrangle, Riverside County, California, that includes: 1. ARC/INFO (Environmental Systems Research Institute) version 7.2.1 double-precision coverages of the various elements of the geologic map 2. A Postscript file to plot the geologic map on a topographic base, and containing a Correlation of Map Units diagram and a Description of Map Units 3. Portable Document Format (.pdf) files of: a. This Readme; includes, in Appendix I, data contained in lkvw_met.txt b. The same graphic as plotted in 2 above. (Test plots from this .pdf do not produce 1:24,000-scale maps. Adobe Acrobat page size settings control map scale.) This release includes features not found in most other digital geologic maps, in that all polygons, lines, and points in the coverage are encoded with detailed, comprehensive, contained in five INFO data tables (.rel) (see Matti and others, 1998a, 1998b, and 1998c for information on how the encoding may be accessed and utilized). No paper map is included in this report, but a PostScript plot file containing an image of the geologic map sheet, topographic base, Correlation of Map Units (CMU), and detailed Description of Map Units (DMU) is. Within the geologic map data package, map units are identified by standard geologic map criteria such as formation name, age, and lithology. Even though this is an author-prepared report, every attempt has been made to closely adhere to the stratigraphic nomenclature of the U. S. Geological Survey. Descriptions of units can be obtained by viewing or plotting the .pdf file (3b above) or plotting the postscript file (2 above). If roads in some areas, especially roads that parallel topographic contours, do not show well on plots of the geologic map, we recommend use of the USGS Lakeview 7.5' topographic quadrangle in conjunction with the geologic map.

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USGS2001

Eagle Mountain Mine: Geology of the former Kaiser Steel Operation in Riverside County, California

This investigation of the Eagle Mountain Mine area, though cursory, revealed new structural, alteration, and stratigraphic relations. Eagle Mountain ores were previously an important source of iron to the western U. S. Ore (where fresh) is magnetite-pyrite rock forming two stratabound horizons virtually continuous for 11 km. Gneissic basement rocks are overlain by two sedimentary units, separated by unconformities. The lower unit contains carbonate rocks and quartzite; the "vitreous quartzite" of previous workers, however, is an alteration feature rather than a stratigraphic one. The upper unit contains thick conglomerates. This layered sequence of rocks is deformed into a west-plunging anticline. Intrusion by Jurassic quartz monzonite apparently followed this deformation. Quartz monzonite forms a branching network of sills, some of which dilate the contact between the upper and lower sedimentary sequences. Intrusion resulted in extensive, mostly-anhydrous skarns, but stratabound iron ore is just as closely related to some other features: regional alteration of quartz monzonite, with iron ore adjacent to little-altered rocks along the boundary between sodic and potassic domains, the two unconformities, which apparently formed stratigraphic traps for precipitation of stratabound iron ores, a north-facing monoclinal plane between folds, which was preferentially replaced. Iron ore replaces a variety of host rocks along the two unconformities, forming massive to globular bodies, and its mineralogy correlates with deuteric alteration features, not anhydrous skarn. Its pyrite contains as much as 3% cobalt. Iron was only one of five elements that showed mobility in this region on a scale that suggests basic crustal processes. The others in probable order of flux magnitude are silica, magnesium, sodium, and potassium, to form regionally distributed “vitreous quartzite”, dolomite, and secondary feldspars, respectively.

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