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Subject
- History46
- Railroads38
- Roads30
- Geology29
- Indians of North America25
- Maps15
- Geology, Structural14
- Geology, Stratigraphic11
- Forest reserves10
- Forests and forestry9
- Geomagnetism9
- National parks and reserves9
- Boundaries8
- Cities and towns8
- Highway planning8
- Indian reservations8
- Administrative and political divisions7
- Canals7
- Geological cross sections7
- Territorial expansion7
