Topic
- Railroad construction & maintenance 2
- Railroad engineering 2
- Steamboats 2
- Transportation 2
- Trees 2
- Aerial photography 1
- Agriculture 1
- Apples 1
- Beer 1
- Boat ramps 1
- Boatbuilding 1
- Bridges--Design and construction 1
- Burning of land 1
- Cafeterias 1
- Canada, Western 1
- Canals 1
- Cartography 1
- Cascade Range 1
- Columbia River 1
- Conservation of natural resources 1