Region
United States
162
Mexico
4
North America
3
Antarctica
2
Columbia River Watershed
2
Developing countries
2
Europe, Eastern
2
Mexican-American Border Region
2
Africa
1
Africa South of the Sahara
1
Africa, Sub-Saharan
1
Arctic regions
1
Asia
1
California
1
Columbia River
1
Columbia River Region
1
Czech Republic
1
Europe
1
Fernald
1
Great Lakes Region (North America)
1
Lancaster County
1
Latin America
1
Louisiana
1
Nevada
1
Oceania
1
Ohio
1
Pennsylvania
1
Soviet Union
1
Texas
1
Tropics
1
Wyoming
1