This publication supports USGS Map I-1970 (the printed map) and DDS-38 (map data on CDROM). It provides an explanation of map units, discussion of geologic features shown on the map, the full list of references (about 850) used to compile the map, and the acknowledgments. Bulletin 1921 may be purchased from the USGS Earth Science Information Center (see the DDS-38 ordering information). Or, you can download a copy here, in PDF format. PDF documents can be viewed with Adobe's free Acrobat Reader. The Bulletin's text and figures are in separate, linked PDF files, and are contained within a gzipped tar file. (Software to extract the document). The PDF file containing only the Bulletin's text also is available:
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