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Spatial Coverage
- United States6
- Powder River Basin (Wyo. and Mont.)4
- Powder River Basin.4
- Middle West3
- San Juan Basin (N.M. and Colo.)2
- San Juan Basin.2
- Black Canyon of the Gunnison National Monument Region1
- Colorado1
- Erie, Lake, Region1
- Gulf Coast (U.S.)1
- Iowa1
- Long Island Sound (N.Y. and Conn.)1
- Michigan1
- Middle Atlantic States1
- Middle West.1
- Ouray Region1
- Southern States1
- Wisconsin1
