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- Forests and forestry 6
- Civilian Conservation Corps (U.S.) 5
- Lichens 4
- Forest fires--Prevention and control 3
- Telephone lines 3
- Fire lookout stations 2
- Ponderosa pine 2
- Agriculture 1
- Airplanes 1
- Burning of land 1
- Conservation of natural resources 1
- Conservation of natural resources--Law and legislation 1
- Game and game-birds 1
- Geological Survey (U.S.) 1
- Groundwater 1
- Izaak Walton League of America 1
- Lakes--Oregon 1
- Land use--Planning 1
- Midge 1
- Oregon State Agricultural College 1