_Geologic Maps._ United States Geological Survey: map of the United
States (1932); map of Colorado (1935). Geologic maps of a few other
states are available; information regarding these may be obtained from
state universities or state geological surveys.
Note: Bulletins of the U.S.G.S. are purchasable from the
Superintendent of Documents, Washington, D. C. Maps are sold by the
Director of the Geological Survey, Washington, D. C.