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- Hydroelectric power plants 58
- Dams 27
- Power-plants 19
- Rivers--Oregon 18
- Water-power 18
- Factories 12
- Hydroelectric power plant retirement 12
- Industrial buildings 12
- Northwestern Electric Company 12
- Spillways 10
- Fishways 7
- Iron and steel bridges 7
- Spokane Falls (Wash. : Waterfall) 6
- Northwest, Pacific 5
- Bodies of water 3
- Conservation of natural resources 3
- Hydroelectric generators 3
- Industrialization 3
- Maps 3
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