This is an Arc/Info database version of USGS Map I-1819 from

F.S. Fisher, D.H. McIntyre and K.M. Johnson, 1992, Geologic Map of the
Challis 1x2 Quadrangle, Idaho
  
The original stable base printing sheets were digitized and attributed for 
Nancy Shock by TechniGraphic System, Inc. of Fort Collins Colorado.  Greg Green
edited and prepared the digital version for release as a gis database.