The United States Department of Agriculture Natural Resources Conservation Service has compiled detailed soils data for approximately 95 percent of the counties in the United States. The soils data contains information such as the texture, drainage, depth, and chemical characteristics of the soil. This data can be accessed by reviewing hard copy Soil Surveys (which can typically be found at the local library or local NRCS office), or online from the NRCS Web Soil Survey.
The University of California Davis Soil Resource Lab recently compiled this data in KML format, which can be viewed directly in Google Earth (using the button below the screenshot), or via a Google Maps interface. Once you zoom in close enough to the ground, you will see the soil unit polygons appear. Click on the dot to open a balloon with detailed information about the soil unit.
There are several other interfaces (such as iPhone/Android apps) available from the UC Davis Soil Resource Lab Soil Web Homepage and it looks like the soils lab is also experimenting with several other methods of visualizing soils data in Google Earth.