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Subject
- Railroads42
- Indians of North America15
- Roads12
- Discovery and exploration11
- Pacific railroads7
- Geology6
- Gold mines and mining6
- Explorations and surveys5
- Gold discoveries5
- Railroad land grants5
- Upper mantle project4
- Discoveries in geography3
- Faults (Geology)3
- Indian reservations3
- Postal service3
- Trails3
- American2
- Earthquakes2
- Geology, Structural2
- Hydrology2
