Clark County, Washington
The most common soil here is Cinebar, on about 22% of the land: a silt loam, smooth, like flour. Olympic and Hesson come next.
About 78% of the land drains well, and 9% stays wet for long stretches; groundwater comes within two feet of the surface under 15% of it.
USDA rates 84% 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: 5% of the land floods occasionally or more.
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 Clark County, Washington, 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 Andisols — soils formed in volcanic ash, very light and porous. 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 Clark County, Washington. 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 |
|---|---|---|---|---|---|
| Hesson clay loam, 0 to 8 percent slopes | 24K | Well drained | C | Somewhat limited | Very limited |
| Cinebar silt loam, 8 to 20 percent slopes | 23K | Well drained | B | Somewhat limited | Somewhat limited |
| Cinebar stony silt loam, 30 to 70 percent slopes | 21K | Well drained | B | Very limited | Very limited |
| Cinebar silt loam, 20 to 30 percent slopes | 20K | Well drained | B | Very limited | Very limited |
| Olympic clay loam, 8 to 20 percent slopes | 18K | Well drained | C | Somewhat limited | Very limited |
| Gee silt loam, 0 to 8 percent slopes | 16K | Moderately well drained | C | Somewhat limited | Very limited |
| Kinney silt loam, 30 to 50 percent slopes | 13K | Well drained | B | Very limited | Very limited |
| Olympic stony clay loam, 3 to 30 percent slopes | 12K | Well drained | C | Very limited | Very limited |
| Olympic stony clay loam, 30 to 60 percent slopes | 11K | Well drained | C | Very limited | Very limited |
| Lauren gravelly loam, 0 to 8 percent slopes | 11K | Well drained | B | Not limited | Very limited |
| Cinebar silt loam, 30 to 70 percent slopes | 11K | Well drained | B | Very limited | Very limited |
| Dollar loam, 0 to 5 percent slopes | 11K | Moderately well drained | C | Very limited | Very limited |
| Hesson clay loam, 8 to 20 percent slopes | 11K | Well drained | C | Somewhat limited | Very limited |
| Olympic clay loam, 30 to 60 percent slopes | 10K | Well drained | C | Very limited | Very limited |
| Hillsboro loam, 3 to 8 percent slopes | 9K | Well drained | B | Not limited | Very limited |
| Hillsboro silt loam, 0 to 3 percent slopes | 8K | Well drained | B | Not limited | Somewhat limited |
| Hillsboro silt loam, 3 to 8 percent slopes | 8K | Well drained | B | Not limited | Somewhat limited |
| Odne silt loam, 0 to 5 percent slopes | 7K | Poorly drained | D | Very limited | Very limited |
| Hillsboro loam, 0 to 3 percent slopes | 7K | Well drained | B | Not limited | Very limited |
| Cinebar stony silt loam, 3 to 30 percent slopes | 7K | Well drained | B | 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 53% of soils are rated "very limited" for dwellings with basements. Specific challenges include steep slopes, poor drainage in some areas. A geotechnical assessment is recommended before building.
Septic Systems
About 84% 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.