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- Croplands 8
- Burning of land 7
- Forests and forestry 6
- Lakes 6
- Willamette River Valley (Or.) 5
- Farms 4
- Mountains 4
- Cities and towns 3
- Cutover lands 2
- Irrigation farming 2
- Lava flows 2
- Smoke 2
- Trees--Diseases and pests 2
- Agricultural experiment stations 1
- Bark beetles 1
- Canneries--Waste disposal 1
- College buildings 1
- Harvester ants 1
- Insect pests 1
- Orchards 1