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- Lectures and lecturing 527
- Oregon--History 168
- University of Oregon 168
- Thomas Condon 161
- Sagan, Carl, 1934-1996 106
- Astronomy 88
- United States. National Aeronautics and Space Administration 65
- Drake, Charles L. 55
- Geology 55
- Charts, diagrams, etc 39
- Rivers--Oregon 36
- Dams 31
- Water--Pollution 20
- Wildlife refuges 20
- Conservation of natural resources 19
- Birds--Conservation 18
- Oregon Wildlife Federation 17
- Salmon 16
- Fishes--Conservation 13
- Izaak Walton League of America 10