This generalized geology dataset was developed as input to a total dissolved solids Spatially Referenced Regressions on Watershed Attributes (SPARROW) model for the Upper Colorado River Basin (UCRB; Kenney and others, 2009) and for a more recent update to that model. The largest source of naturally generated dissolved solids in streams of the UCRB is the rocks underlying stream basins, particularly rocks high in dissolvable minerals. For the purposes of modeling, the scale of the geologic dataset optimally should be similar to the scale of the stream-catchment network used in the model but simplified to reduce the number of geologic units represented in the data. This dataset was developed to meet both scale and simplification requirements by grouping lithologic units found in five 1:500,000-scale state geologic maps into broad lithologic units based on 1:2,500,000-scale King and Beikman Geology. References cited: Kenney, T.A., Gerner, S.J., Buto, S.G., and Spangler, L.E., 2009, Spatially referenced statistical assessment of dissolved-solids load sources and transport in streams of the Upper Colorado River Basin: U.S. Geological Survey Scientific Investigations Report 2009-5007, 50 p. Available at http://pubs.usgs.gov/sir/2009/5007.