| Quaternary Basin Fill and Alluvial Aquifers (Qs) |
| Tertiary Sedimentary Aquifer (Ts) |
| Fort Union Aquifer (Tfu) |
| Igneous Rock Aquifer (TKig) |
| Livingston Aquifer (Klvgs) |
| Fox Hills-Hell Creek Aquifer (Kfhhc) |
| Cretaceous Shales Confining Unit (Kshale) |
| Judith River Aquifer (Kjr) |
| Eagle Aquifer (Kegle) |
| Kootenai Aquifer (Kkotn) |
| Sedimentary Rock Aquifer (MPsed) |
| Madison Aquifer (Mmdsn) |
| Lower Paleozoic Aquifer (Pzl) |
| Fractured Bedrock Aquifer (PCfb) |
| Rivers, Lakes, and Reservoirs (W) |