Dewey County, South Dakota
The most common soil here is Opal, on about 18% of the land: a clay, sticky when wet and rock-hard when dry. Sansarc and Dupree come next.
About 89% of the land drains well.
USDA rates 90% of the land very limited for a standard septic drain field, and 78% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: bedrock lies within 40 inches under 77% of it.
Soils change over short distances, so look up an address below for the soil at that exact spot and the reasons behind each rating.
The soils you're most likely standing on
The biggest named soils in Dewey County, South Dakota, each drawn five feet deep from its official USDA description, in its recorded colors.
Dots mark gravel; white flecks mark lime. Shares are by acres across the survey area, and each mapped patch usually mixes several of these soils.
The biggest mapped areas
The dominant drainage class is Well drained and the dominant hydrologic group is D (very slow infiltration, high runoff). The most common soil order is Mollisols — grassland soils with a thick, dark, fertile topsoil rich in organic matter. 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 Dewey County, South Dakota. Search your address to find the exact soil composition, drainage, and series details at your specific location.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Sansarc-Opal clays, 9 to 25 percent slopes | 345K | Well drained | D | Very limited | Very limited |
| Water | 98K | Not rated | Not rated | ||
| Opal clay, 3 to 9 percent slopes | 83K | Well drained | D | Very limited | Very limited |
| Sansarc-Dupree, acid, clays, 6 to 25 percent slopes | 82K | Well drained | D | Very limited | Very limited |
| Opal-Sansarc clays, 6 to 15 percent slopes | 78K | Well drained | D | Very limited | Very limited |
| Dupree-Opal clays, 3 to 9 percent slopes | 65K | Well drained | D | Very limited | Very limited |
| Vebar fine sandy loam, 3 to 6 percent slopes | 54K | Well drained | B | Somewhat limited | Very limited |
| Morton silt loam, 2 to 6 percent slopes | 44K | Well drained | C | Somewhat limited | Very limited |
| Rhoades-Daglum complex, 0 to 6 percent slopes | 37K | Moderately well drained | D | Very limited | Somewhat limited |
| Wayden-Moreau silty clays, 25 to 40 percent slopes | 36K | Well drained | D | Very limited | Very limited |
| Regent-Ridgeview silty clay loams, 2 to 6 percent slopes | 36K | Well drained | D | Very limited | Very limited |
| Opal-Hurley complex, 0 to 9 percent slopes | 35K | Well drained | D | Very limited | Very limited |
| Chantier clay, 2 to 9 percent slopes | 33K | Well drained | D | Very limited | Very limited |
| Cabba-Lantry complex, 25 to 40 percent slopes | 26K | Well drained | D | Very limited | Very limited |
| Hurley-Slickspots complex, 2 to 9 percent slopes | 26K | Well drained | D | Very limited | Very limited |
| Morton-Lantry silt loams, 2 to 9 percent slopes | 25K | Well drained | C | Somewhat limited | Very limited |
| Belfield-Reeder loams, 2 to 6 percent slopes | 25K | Well drained | C | Very limited | Very limited |
| Moreau-Wayden silty clays, 9 to 25 percent slopes | 24K | Well drained | D | Very limited | Very limited |
| Promise-Wendte clays, channeled, occasionally flooded | 22K | Well drained | D | Very limited | Very limited |
| Promise clay, 3 to 6 percent slopes | 18K | Well drained | D | Very limited | Very limited |
Soil Orders in This Area
The USDA classifies every soil into one of 12 soil orders. Here are the dominant orders found in this survey area.
What This Means
Building & Foundations
About 78% of soils are rated "very limited" for dwellings with basements. Specific challenges include shallow bedrock, steep slopes. A geotechnical assessment is recommended before building.
Septic Systems
About 90% 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.