May be this is just old news for you but possibly it is useful for someone out there. After browsing for basic geological maps of the United States, I discovered a page that solved all of my problems. Here at a page provided by the USGS, you can download geological maps of all states as shapefiles or kml-layer for Google Earth. It is very easy way to find localities for the next fieldtrip for instance.
The north-western area of the Utah Geology layer displayed in Google Earth
