| Abbreviation | Definition |
|---|---|
| UMWA | United Mine Workers of America |
| UMWT | Upper Mon Water Trail |
| UOV | Upper Ohio Valley |
| UPRB | Upper Paraguay River Basin |
| UPT | Uniformitarian Plate Tectonics |
| USA | United States of America |
| USB | Useless Steam Blowhole |
| USCGS | United States Coast and Geodetic Survey |
| USDW | Underground Source of Drinking Water |
| USDW(S} | underground source(s) of drinking water |
| USG | United States Gypsum |
| USLW | Upper Susquehanna- Lackawanna Watershed |
| USNK | Upper Snake River |
| USRB | Upper Snake River Basin |
| USTZ | Un- Supported Transition Zone |
| UTR | Un-Translated Region |
| UU | Undrain UnConsolidation Triaxial Test |
| UVO | Usu Volcano Observatory |
| UWRB | Upper White River Basin |
| UYB | Upper Yangtze Basin |