Region
North America
31
United States
9
Colorado
7
Montana
7
California
6
Kansas
4
Nevada
4
Alaska
3
Minnesota
3
Connecticut
2
Front Range (Colo. and Wyo.)
2
Maine
2
Massachusetts
2
Missouri
2
New Mexico
2
New York (State)
2
Oregon
2
Texas
2
Utah
2
Virginia
2
Wyoming
2
Atlantic Coast
1
Berkshire County
1
Champlain Valley
1
Clear Creek County
1
Delaware
1
Gilpin County
1
Gunnison County
1
Humboldt Range
1
Humboldt Range (Nev.)
1
Idaho
1
Illinois
1
Kentucky
1
Lincoln County
1
Michigan
1
Nevada National Security Site (Nev.)
1
New Madrid
1
Oklahoma
1
Owens Lake
1
Oxford County
1
Pacific Coast
1
Pennsylvania
1
Preston
1
Rhode Island
1
San Francisco Bay Area
1
Seward Peninsula
1
South Dakota
1
Southwestern States
1
Taos County
1
Washington (State)
1
more ...