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Subject (Region)
- District of Columbia38
- Nicaragua Canal (Nicaragua)8
- Nicaragua7
- Cacapon River (West Virginia)2
- Chesapeake and Ohio Canal (District of Columbia/Maryland/West Virginia)2
- Harpers Ferry, West Virginia2
- Maryland2
- Ohio River2
- Pennsylvania2
- Potomac River2
- California1
- Dismal Swamp Canal (Virginia)1
- Norfolk, Virginia1
- Point of Rocks, Maryland1
- South (U.S.)1
- Virginia1