The U.S. Geological Survey (USGS) has generated a new classification and map of the lithology of surficial
materials for the contiguous United States. This was developed as part of an effort to map standardized,
terrestrial ecosystem distributions for the nation using a classification developed by
NatureServe (Comer and others, 2003). This ecosystem mapping methodology, which delineates ecosystems
by mapping and integrating their major structural components, was first developed for South
America (Sayre and others, 2008) and is now being implemented globally (Sayre and others, 2007). Surficial
lithology strongly influences the differentiation and distribution of terrestrial ecosystems,
and is one of the key input layers in the ecosystem delineation process.
These surficial lithology classes were derived from the USGS map "Surficial Materials in the
Conterminous United States", which was based on texture, internal structure, thickness and
environment of deposition or formation of materials (Soller and Reheis, 2004). This original
map was produced from a compilation of regional surficial and bedrock geology source maps
using broadly defined common map units for the purpose of providing an overview of the
existing data and knowledge (Soller and Reheis 2004). For the national terrestrial ecosystem
mapping effort, the original 28 lithology classes were reclassified into a set of 18 lithologies
that typically control or influence the distribution of vegetation types (Kruckeberg, 2002).