Surficial geology of the Southwest Principal Aquifers (SWPA) study
This is a 100-meter cell resolution raster dataset consisting of 1:750,000-scale surficial geology 
for California and 1:500,000-scale for Nevada, and parts of Utah, Colorado, New Mexico, and 
Arizona.  This data set was aggregated from a compilation of geologic maps of the Southwest 
Regional GAP Analysis Project …