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USGS · 70211265

Geology

John C. Reed·Charles A. Bush
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Abstract

This map shows the ages and types of rocks that lie at or near the land surface throughout the United States. It does not show surficial materials such as soil and glacial deposits, except where Quartenary sedimentary materials cover extensive areas and obscure underlying bedrock materials. The map is a generalization and simplification of the "Geologic Map of North America," published by the Geological Society of America in 2005. A more complete description of the map and discussion of major geologic features it portrays are available as U.S. Geological Survey Circular 1300 (in press).

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National Atlas of the United States of AmericaReport
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 17.866361230891894° to 71.35706654962706° latitude; -178.2421875° to -65.2587890625° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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John C. Reed, Charles A. Bush. 2007. Geology. https://doi.org/10.3133/70211265

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USGS1984

Surficial geology

Surficial materials are those at or near the Earth's surface. They constitute, by far, the largest and most used part of the ground around us. Areas not covered by surficial deposits--bare bedrock--form probably less than 5 percent of our land surface. Most surficial deposits are composed of poorly consolidated clay, silt, sand, or gravel-sized particles that are produced chiefly by erosion and are transported by and finally deposited by water, wind, or ice, but are also partly produced by the in-situ weathering of bedrock. The major genetic categories are shown on the map by various colors; the principal compositional types in each category are indicated by patterns. Colors, patterns, and letter symbols are given in the explanation which follows this summary description. Surficial deposits have characteristics important to our environment--water-bearing properties, mineral resources, and suitability as a natural foundation for buildings. They are also susceptible to flooding, erosion, ground subsidence, land slides, and earthquakes.

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