Subject Region
United States
California
3
Afghanistan
2
Coeur d'Alene Mining District
2
Coeur d'Alene Mining District (Idaho)
2
Hiroshima-shi (Japan)
2
Idaho
2
India
2
Los Angeles
2
Nicaragua
2
Pakistan
2
Virginia
2
Butler County
1
Colorado
1
Denmark
1
Detroit
1
Garfield County
1
Iowa
1
Marcellus Shale
1
Mexico, Gulf of
1
Michigan
1
Middle East
1
New York
1
New York (State)
1
Oakland
1
Rocky Mountains
1
San Juan Basin (N.M. and Colo.)
1
Soviet Union
1
Sweden
1