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Southern California Areal Mapping Project

 

Classification of Surficial Materials

Surficial materials--geologic materials that have accumulated at the land surface over the last one million years or so--are widespread throughout southern California. These are relatively unconsolidated materials that mantle the ground surface of valleys and hillslopes, or that form the uppermost fillings of valleys and alluvial fans. Typical examples include:

 

  • sand and gravel deposits that occur in river and creek bottoms or that form valley floors;
  • loose rubble that lies on hillslopes;
  • landslides and other slope-failure materials that occur on hillsides;
  • wind-deposited sand dunes and sand sheets.

The Southern California Areal Mapping Project (SCAMP) is developing a uniform scheme to classify and map the myriad different types of surficial materials that occur in southern California. The provisional classification uses three kinds of information to distinguish among geologic-map units of such deposits:

  • physical properties and lithologic features (including consolidation and induration, depositional fabric, grain size, sorting, bed forms, matrix support versus grain support);
  • geologic age (as determined from pedogenic-soil characteristics, desert varnish and pavement, vegetation, degree of incision, radiometric analyses, paleontology, magnetostratigraphy);
  • genesis and geomorphic setting (physiographic setting) and mode of origin (alluvial-fan, slope-wash, pediment-veneer, estuarine, etc.).
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URL: http://geomaps.wr.usgs.gov/archive/scamp/html/sc_surf.html
This site last updated September 3, 2004 (ps)

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