Boulder County Area, Colorado
The most common soil here is Nunn, on about 11% of the land: a clay loam, firm and a little sticky. Ascalon and Valmont come next.
About 86% of the land drains well, and 8% stays wet for long stretches; groundwater comes within two feet of the surface under 4% of it.
USDA rates 78% of the land very limited for a standard septic drain field, and 53% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 8% of the land floods occasionally or more, and bedrock lies within 40 inches under 38% 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 Boulder County Area, Colorado, 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 C (slow infiltration, moderate 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 Boulder County Area, Colorado. 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 |
|---|---|---|---|---|---|
| Juget-Rock outcrop complex, 9 to 55 percent slopes | 21K | Somewhat excessively drained | D | Very limited | Very limited |
| Nunn clay loam, 1 to 3 percent slopes | 16K | Well drained | C | Somewhat limited | Very limited |
| Fern Cliff-Allens Park-Rock outcrop complex, 15 to 60 percent slopes | 13K | Well drained | A | Very limited | Very limited |
| Ascalon sandy loam, 0 to 3 percent slopes | 12K | Well drained | B | Not limited | Somewhat limited |
| Lefthand, very stony-Littlejames, extremely bouldery complex, 20 to 55 percent slopes | 12K | Somewhat excessively drained | B | Very limited | Very limited |
| Nederland very cobbly sandy loam, 1 to 12 percent slopes | 11K | Well drained | B | Very limited | Very limited |
| Niwot loam, 0 to 1 percent slopes | 9K | Poorly drained | C/D | Very limited | Very limited |
| Terrace escarpments | 8K | Excessively drained | A | Very limited | Very limited |
| Water | 8K | Not rated | Not rated | ||
| Nunn clay loam, 0 to 1 percent slopes | 7K | Well drained | C | Somewhat limited | Very limited |
| Rock outcrop | 7K | D | Not rated | Not rated | |
| Boulder, bouldery-Sylvandale complex, 9 to 45 percent slopes | 6K | Well drained | C | Very limited | Very limited |
| Valmont clay loam, 1 to 3 percent slopes | 6K | Well drained | C | Not limited | Very limited |
| Valmont cobbly clay loam, 1 to 5 percent slopes | 6K | Well drained | C | Not limited | Not limited |
| Samsil-Shingle complex, 5 to 25 percent slopes | 6K | Well drained | D | Very limited | Very limited |
| Carterlake, stony-Rock outcrop complex, 15 to 55 percent slopes | 5K | Well drained | D | Very limited | Very limited |
| Nunn clay loam, 3 to 5 percent slopes | 5K | Well drained | C | Somewhat limited | Very limited |
| Baller, bouldery-Rabbitmountain complex, 9 to 35 percent slopes | 5K | Well drained | D | Very limited | Very limited |
| Heldt clay, 0 to 3 percent slopes | 5K | Well drained | C | Somewhat limited | Very limited |
| Ascalon sandy loam, 3 to 5 percent slopes | 5K | Well drained | B | Not limited | Somewhat 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 53% 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 78% 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.