What are geologic maps and where can I get them?
Geologic maps show the distribution of features such as rock formations, alluvial deposits, faults, and folds at or near the surface of the earth. There are generally two kinds of geologic maps—bedrock and surficial. Bedrock geologic maps show where various bedrock types, such as sandstone, limestone, or diabase, are present, either at the earth’s surface or immediately beneath unlithified sediments. Surficial geologic maps display the distribution of various unlithified sediments, such as glacial and stream deposits, that are on top of the bedrock. To learn more about geologic maps and symbols and to view colorful examples, please see wrgis.wr.usgs.gov/docs/parks/gmap/. The Survey has published many geologic maps, including a large wall map of the state (Map 1). A digital version of the state geologic map is available on the Survey’s web site at /topogeo/map1/digital.aspx. A popular item has been the Survey’s Map 61, a compilation of bedrock geologic maps of quadrangles that have not
