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- Agriculture 1
- American wit and humor, Pictorial 6
- Bodies of water 32
- Canals--Design and construction--Costs 29
- Conservation of natural resources 3
- Dalles Dam (Or. and Wash.) 1
- Dams--Design and construction 28
- Electric power transmission 1
- Fisheries 2
- Forests and forestry 1
- Grand Coulee Dam (Wash.) 1
- Hydroelectric power plants 1
- Hydroelectric power plants--Law and legislation 1
- Irrigation projects 1
- Irrigation 1
- Locks (Hydraulic engineering)--Oregon 3
- Maps 2
- Mineral industries 1
- National parks and reserves 1
- Northwest, Pacific 32