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Topic
- Bodies of water 88
- Rivers 80
- Northwest, Pacific 71
- River engineering 34
- Photography 31
- United States. Congress--Records and correspondence 30
- River surveys 29
- Riparian areas 23
- River channels 22
- Harbors 21
- Aerial photographs 19
- Dams 19
- West (U.S.) 17
- Rapids 14
- Mountains 13
- Canals 12
- United States--Armed Forces--Organization--Charts, diagrams, etc 10
- Formations (Geology) 8
- Conservation of natural resources 7
- Maps 7