National Cartographic Information Center 
US Geological Survey 
Department of the Interior 
MS 507, National Center 
12201 Sunrise Valley Drive 
Reston, VA 22092 
(703) 860-6045, FTS 928-6045 
Kind of Data 
Geologic Maps 
Location: The 50 states and selected territories 
Dates: All of the maps are periodically revised and/or 
field checked by the USGS. 
Description of Data: Geologic maps show the distribution of rocks and surfi- 
cial material by age, and their physical and structural relations with one 
another. Inferences can be drawn from these maps about an area's geologic 
history, geologic processes, orientation of rock layers, faults, fractures, 
and shape of rock bodies beneath the surface. 
Geologic maps published by the USGS range in scale from 1:20,000 to 
1:2,500,000 depending on the type of information to be portrayed and the- 
purpose of the mapping (see table on next page). 
Geologic maps at 1:250,000 or larger scales are available for nearly 
50 percent of the United States. Most of the maps are contained in the 
Geologic Quadrangle Maps series. These maps cover an individual 7-1/2- (scale 
1:24,000) or 15- (scale 1:62,500) min quadrangle. Geologic or sections of 
individual quadrangles are published in other series and make up a smaller 
fraction of all geologic maps of the United States. The maps may be supple- 
mented by structure sections, columnar sections, and other graphic means of 
presenting geologic data, plus a brief explanatory text. There are well over 
1,500 geologic quadrangle maps now available in the United States. 
There is also a wide range of special geologic maps for specific pur- 
poses. For example, maps are prepared, generally at a scale of 1:7,500,000, 
that are useful for understanding environmental problems and for making deci- 
sions on land use and mineral and energy resource development on a national 
scale. The following maps of the National Environmental Overview Program have 
been completed in preliminary form: 
(a) Map showing areas of Karst topography and related terrains. 
(b) Map showing areas subject to volcanic hazards. 
(c) Map showing possible areas of landslides. 
(d) Map showing present and proposed nuclear reactor sites. 
(e) Map showing streams with flow rates of 300 ft?/sec or more. 
(£) Map showing surficial clay, sand, silt, and gravel deposits. 
VIII-4 
