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- Bodies of water 394
- Rivers 292
- Northwest, Pacific 270
- West (U.S.) 159
- Photography 132
- River engineering 115
- Explorers 88
- Riparian areas 62
- Discovery and exploration 59
- Railroad engineering 49
- Canada, Western 43
- Aerial photographs 41
- Mountains 41
- Transportation 35
- Rapids 34
- River surveys 32
- United States. Congress--Records and correspondence 32
- Water resources development 32
- Canals--Design and construction--Costs 30
- Dams--Design and construction 30
