Targhee National Forest, Idaho and Wyoming
The most common soil here is Koffgo, on about 11% of the land: a ashy silt loam, smooth, like flour. Edgway and Fritz come next.
About 90% of the land drains well; groundwater comes within two feet of the surface under 4% of it.
USDA rates 94% of the land very limited for a standard septic drain field, and 76% 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 15% 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 Targhee National Forest, Idaho and Wyoming, 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 B (moderate infiltration). 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 Targhee National Forest, Idaho and Wyoming. 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 |
|---|---|---|---|---|---|
| Edgway-Jumpstart-Tophat complex, 15 to 50 percent slopes | 118K | Well drained | C | Very limited | Very limited |
| Juliette-Fritz association, 40 to 70 percent slopes | 99K | Well drained | B | Very limited | Very limited |
| Koffgo-Rhylow-Povey complex, 35 to 60 percent slopes | 90K | Well drained | B | Very limited | Very limited |
| Islandpark-Potrmound-Spliten complex, 0 to 35 percent slopes | 79K | Well drained | B | Not limited | Very limited |
| Gany-Fritz association, 40 to 70 percent slopes | 68K | Well drained | B | Very limited | Very limited |
| Lagall-Povey-Fritz complex, 35 to 70 percent slopes | 64K | Well drained | B | Very limited | Very limited |
| Edgway very gravelly loam, 15 to 40 percent slopes | 61K | Well drained | C | Very limited | Very limited |
| Koffgo-Koffgo, low effective precipitation-Rock outcrop complex, 40 to 70 percent slopes | 60K | Well drained | B | Very limited | Very limited |
| Edgway-Koffgo-Povey association, 15 to 50 percent slopes | 51K | Well drained | B | Very limited | Very limited |
| Flatstone-Koffgo complex, 2 to 15 percent slopes | 43K | Well drained | B | Somewhat limited | Very limited |
| Meegero-Monida complex, 20 to 50 percent slopes | 43K | Well drained | B | Very limited | Very limited |
| Rhylow-Fitzwil association, 4 to 40 percent slopes | 42K | Well drained | A | Very limited | Very limited |
| Huckridge-Koffgo-Povey complex, 4 to 50 percent slopes | 39K | Well drained | B | Very limited | Very limited |
| Koffgo ashy silt loam, 4 to 15 percent slopes | 38K | Well drained | B | Somewhat limited | Very limited |
| Dashiki-Lasac association, 2 to 25 percent slopes | 37K | Well drained | A | Not limited | Very limited |
| Yodal gravelly loam, 35 to 60 percent slopes | 36K | Well drained | B | Very limited | Very limited |
| Lagall very stony ashy loam, 25 to 50 percent slopes | 36K | Well drained | B | Very limited | Very limited |
| Winegar-Bradco complex, 4 to 15 percent slopes | 33K | Well drained | B | Somewhat limited | Somewhat limited |
| Gany-Katpa-Fritz complex, 40 to 70 percent slopes | 32K | Well drained | B | Very limited | Very limited |
| Rubble land-Haplocryepts-Rock outcrop complex, 40 to 70 percent slopes | 31K | A | 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 76% 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 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.