Region
United States
21
California
3
Colorado
3
North Carolina
3
Pennsylvania
3
West Virginia
3
Merced County
2
China
1
Delaware
1
Developing countries
1
Douglas County
1
Douglas County (Nev.)
1
Ecuador
1
Fort Berthold Indian Reservation
1
Georgia
1
Hawaii
1
Jefferson County
1
McDowell County
1
Mexico
1
Missouri River Watershed
1
Morris Lake (N.J.)
1
Nebraska
1
Nevada
1
New Jersey
1
New York
1
New York (State)
1
Newton
1
North Dakota
1
Oklahoma
1
Ozark Mountains
1
Pike County
1
Rio Grande (Colo.-Mexico and Tex.)
1
Rio Grande Watershed (Colo.-Mexico and Tex.)
1
San Bernardino County
1
Sierra Nevada (Calif. and Nev.)
1
Warminster
1
West (U.S.)
1
Willow Grove
1