Stillwater County Area, Montana
The dominant drainage class is Well drained and the dominant hydrologic group is D (very slow infiltration, high runoff). This report summarizes the major soil map units across the survey area to help you understand what to expect when buying, building, or gardening in Stillwater County Area, Montana.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Tanna-Rentsac complex, 4 to 15 percent slopes | 143K | Well drained | D | Somewhat limited | Very limited |
| Yawdim-Lambeth-Rock outcrop association, steep | 123K | Well drained | D | Very limited | Very limited |
| Hilger-Castner-Rock outcrop complex, 25 to 60 percent slopes | 52K | Well drained | D | Very limited | Very limited |
| Tanna clay loam, 2 to 8 percent slopes | 47K | Well drained | D | Somewhat limited | Very limited |
| Wayden-Castner association, steep | 41K | Well drained | D | Very limited | Very limited |
| Birney-Yawdim-Rock outcrop association, steep | 38K | Well drained | B | Very limited | Very limited |
| Lambeth-Yawdim complex, 4 to 15 percent slopes | 33K | Well drained | C | Somewhat limited | Very limited |
| Tanna-Beenom complex, 4 to 8 percent slopes | 33K | Well drained | D | Somewhat limited | Very limited |
| Absarokee-Sinnigam complex, 15 to 50 percent slopes | 27K | Well drained | D | Very limited | Very limited |
| Absarokee-Sinnigam clay loams, 8 to 15 percent slopes | 25K | Well drained | C | Very limited | Very limited |
| Lardell clay loam, 0 to 2 percent slopes | 25K | Somewhat poorly drained | C | Very limited | Very limited |
| Bonfri-Lambeth complex, 2 to 8 percent slopes | 21K | Well drained | C | Somewhat limited | Very limited |
| Winkler-Hilger-Rock outcrop association, steep | 21K | Somewhat excessively drained | A | Very limited | Very limited |
| Absarokee-Sinnigam clay loams, 2 to 8 percent slopes | 19K | Well drained | C | Very limited | Very limited |
| McKenzie clay, saline | 15K | Poorly drained | D | Very limited | Very limited |
| Absher silty clay loam, 0 to 8 percent slopes | 14K | Well drained | D | Somewhat limited | Not limited |
| Lonna silt loam, 2 to 8 percent slopes | 13K | Well drained | B | Not limited | Somewhat limited |
| Absarokee clay loam, 2 to 8 percent slopes | 12K | Well drained | C | Very limited | Very limited |
| Torrifluvents-Camborthids association, gently sloping | 12K | Not rated | Not rated | ||
| Work loam, 4 to 8 percent slopes | 12K | Well drained | C | Somewhat limited | Very limited |
What This Means
Building & Foundations
About 54% of soils are rated "very limited" for dwellings with basements. Specific challenges include shallow bedrock, steep slopes, poor drainage in some areas, flood-prone areas. A geotechnical assessment is recommended before building.
Septic Systems
About 94% of soils are rated "very limited" for septic absorption fields. Despite good drainage overall, limitations may stem from shallow bedrock, steep slopes, or seasonal conditions. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.
Gardening & Agriculture
Well-drained soils on sloped terrain — good for most plants but watch for erosion. Terracing, contour planting, and mulching help retain moisture and topsoil. Drip irrigation is more effective than sprinklers on slopes.