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Topic
- Bodies of water 41
- Rivers 29
- Canals--Design and construction--Costs 26
- Dams--Design and construction 26
- Transportation 26
- West (U.S.) 26
- Northwest, Pacific 25
- Water resources development 25
- Oregon--History 5
- Docks 4
- Harbors 4
- Ships 4
- Aerial photography 3
- Buildings 3
- Cities and towns 3
- Electric power production 3
- Electric power-plants 3
- Port of Portland (Or.) 3
- Roads 3
- Shipbuilding industry 3
