Geology by J.E. Harrison, J.E. Cressman, and J.W. Whipple (1992). Initial 
digitizing by EROS Data Center (pre-1994). Digital database by H.Z. Kayser
(Information Systems Support, Inc.), P.D. Derkey (USGS), assisted by R.J. 
Miller (USGS). Database approved for publication October 5, 2000.
