Region
United States
52
China
2
Pennsylvania
2
Texas
2
Washington (D.C.)
2
Yellowstone National Park
2
Allegheny River (Pa. and N.Y.)
1
Arizona
1
Big Thicket National Preserve (Tex.)
1
Cave Creek Canyon (Ariz.)
1
Delaware
1
Jemez National Recreation Area (N.M.)
1
Lamprey River (N.H.)
1
New Hampshire
1
New Mexico
1
Pelican Island (Galveston County)
1
Pelican Island (Galveston County, Tex.)
1
Saint Croix
1
Salt River Bay National Historical Park and Ecological Preserve (United States Virgin Islands)
1
Soviet Union
1
United States Virgin Islands
1
Virginia
1
White Clay Creek (Pa. and Del.)
1