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- Rapids 16
- Columbia River 15
- Waterfalls 14
- Oregon, Eastern 12
- Iron and steel bridges 4
- Irrigation canals and flumes 4
- Buildings--Irrigation systems 3
- Indians of North America 3
- Rivers 2
- Boatbuilding 1
- Boats and boating 1
- Bodies of water 1
- Canada, Western 1
- Canals 1
- Cartography 1
- Columbia River Gorge (Or. and Wash.) 1
- Dams--Surveying 1
- Discoveries in geography 1
- Discovery and exploration 1
- Eddies 1