Soil series profile
Twilight soil series
Twilight is a well drained soil with a fine sandy loam surface, mapped on 802,822 acres in 34 counties across 3 states. Hydrologic group B.
- Drainage class
- Well drained 100% of mapped acres
- Hydrologic group
- B >99% of mapped acres
- Typical topsoil pH
- 7.2 neutral · range 7.0–7.6
- Mapped area
- 803k acres in 34 counties, 3 states
Typical Twilight profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–3 in (A) | Fine sandy loam | 7.2 | 12% | 65% | 2% |
| 3–10 in (Bw) | Fine sandy loam | 7.2 | 12% | 63% | 0.75% |
| 10–35 in (BC) | Fine sandy loam | 7.8 | 12% | 63% | 0.25% |
| 35–55 in (Cr) | Bedrock | Not reported | Not reported | Not reported | Not reported |
What this means
What Twilight soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Twilight soils is neutral: pH 7.2 (most land between 7.0 and 7.6), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 100% of mapped Twilight acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is fine sandy loam (86% of mapped Twilight acres).
100% of mapped Twilight acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.
For a septic system
For conventional septic absorption fields, NRCS rates 100% of the acres in mapped Twilight soils very limited, 0% somewhat limited and 0% not limited.
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Twilight soil is found
Mapped acres
Twilight is mapped in Montana, South Dakota and Wyoming.
| County | Acres | Share of county land |
|---|---|---|
| Harding County, SD | 139,511 | 8.2% |
| Garfield County, MT | 121,872 | 4.2% |
| Meade County, SD | 64,399 | 2.9% |
| Carter County, MT | 52,267 | 2.7% |
| Perkins County, SD | 52,165 | 2.8% |
| Fallon County, MT | 38,969 | 3.8% |
| Butte County, SD | 37,886 | 2.6% |
| Custer County, MT | 36,384 | 1.5% |
| Musselshell County, MT | 31,830 | 2.7% |
| McCone County, MT | 30,859 | 1.8% |
| Rosebud County, MT | 29,058 | 0.6% |
| Dawson County, MT | 26,989 | 1.8% |
| Big Horn County, MT | 21,500 | 0.5% |
| Petroleum County, MT | 18,865 | 1.8% |
| Golden Valley County, MT | 16,596 | 2.3% |
| Yellowstone County, MT | 15,872 | 0.9% |
| Phillips County, MT | 13,814 | 0.4% |
| Prairie County, MT | 12,293 | 1.1% |
| Chouteau County, MT | 10,224 | 0.4% |
| Blaine County, MT | 6,830 | 0.2% |
| Teton County, MT | 4,742 | 0.4% |
| Richland County, MT | 4,567 | 0.3% |
| Treasure County, MT | 3,557 | 0.6% |
| Wheatland County, MT | 3,221 | 0.4% |
| Campbell County, WY | 2,221 | 0.1% |
| Pondera County, MT | 1,857 | 0.2% |
| Hill County, MT | 1,816 | 0.1% |
| Stillwater County, MT | 946 | 0.1% |
| Sweet Grass County, MT | 689 | 0.1% |
| Powder River County, MT | 502 | 0.0% |
| Fergus County, MT | 179 | 0.0% |
| Liberty County, MT | 141 | 0.0% |
| Crook County, WY | 127 | 0.0% |
| Park County, WY | 74 | 0.0% |
Septic absorption fields
NRCS rating, share of Twilight acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 100.0% |
Drainage, water table and flooding
Share of Twilight acres
- Depth to seasonal high water table
- None reported within about 6.5 feet (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 5–30% (median 12%).
- Topsoil organic matter
- Median 2%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 100.0% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 99.7% |
| C: slow infiltration | 0.3% |
| D: very slow infiltration (clayey, shallow or wet) | 0.0% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.0% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- All map unit components named Twilight (component kind "Series") in SSURGO: 802,822 acres.
- Method
- Shares are by mapped acres of Twilight components. The profile comes from the single largest Twilight component. Full methodology.