Topic
- Mills26
- Rainbow Bridge (Utah)25
- Waterwheels25
- Yucatan (Mexico : State)25
- Kentucky24
- Floods23
- Florida23
- Canyon de Chelly National Monument (Arizona)22
- Power plants22
- Pueblo architecture22
- Archaeological sites21
- Kentucky River (Ky.)21
- Hoover Dam (Ariz. and Nev.)20
- Nevada20
- Cliff-dwellings19
- Dam construction19
- Volcanoes19
- Mesa Verde National Park (Colo.)17
- Volcanic rock17
- Bridges16