Region
West (U.S.)
United States
21
Colorado
14
Colorado River Watershed (Colo.-Mexico)
8
California
3
Rocky Mountains
3
Southern States
3
Colorado River (Colo.-Mexico)
2
Great Basin
2
Middle West
2
Northeastern States
2
Alaska
1
Arizona
1
Asia
1
Australia
1
British Columbia
1
California National Historic Trail
1
Canada
1
Canada, Western
1
Great Plains
1
Hawaii
1
Hoover Dam (Ariz. and Nev.)
1
Mormon Pioneer National Historic Trail
1
Nevada
1
New Mexico
1
Oregon National Historic Trail
1
Phosphoria Formation
1
Pony Express National Historic Trail
1
Southwestern States
1
United States Highway 66
1