HomeSoil seriesArmstrong
Armstrong soil series
Armstrong soils cover 1,533,734 mapped acres, mostly in Missouri and Iowa. USDA rates shrink-swell a limit for houses without basements on 99% of that land, and a shallow water table a limit for basements on over 99%.
It is the leading soil series by area in 8 of the counties and cities on this site, including Linn County, MO; Adair County, MO; Chariton County, MO.
SSURGO survey versions to August 5, 2026 · series description revised 2017-08
of its land: shrink-swell limits houses without basements
of its land: a shallow water table limits basements
median highest linear extensibility (6% and up is high)
median highest clay content in the top 150 cm
USDA's description
The Armstrong series consists of very deep, somewhat poorly drained soils formed in 25 to 50 centimeters of hillslope sediments or loess and in the underlying paleosol weathered from till. These soils are on side slopes and summits of interfluves on till plains. Slope ranges from 2 to 25 percent. Mean annual air temperature is about 11 degrees C. Mean annual precipitation is about 940 millimeters.
Source: USDA NRCS series description (OSD) for Armstrong, revised 2017-08. Read it.
Engineering properties
| Mapped area (SSURGO) | 1,533,734 acres |
| Shrink-swell limits houses without basements | 99.5% |
| Shallow water table limits basements | 100.0% |
| Very limited for septic absorption fields | 100.0% |
| Most common drainage class | Somewhat poorly drained |
| Most common hydrologic soil group | D |
| Taxonomic class | Fine, smectitic, mesic Aquertic Hapludalfs |
| Type location | Major Land Resource Area (MLRA) 109-Iowa and Missouri Heavy Till Plain, Appanoose County, Iowa |
Where Armstrong is mapped
| State | Mapped acres |
|---|---|
| Missouri | 1,230,112 |
| Iowa | 303,622 |
Places where Armstrong leads
Counties and cities where Armstrong covers more mapped land than any other series.
| Place | Share of mapped land |
|---|---|
| Linn County, MO | 35% |
| Adair County, MO | 22% |
| Chariton County, MO | 20% |
| Scotland County, MO | 20% |
| Knox County, MO | 19% |
| Clark County, MO | 17% |
| Macon County, MO | 16% |
| Marion County, MO | 12% |
Other places where Armstrong is a main soil
Counties and cities where Armstrong is among the six soil series covering the most mapped land, but not the first. Share of the place's mapped land.
Counties
- Sullivan County, MO 23%
- Schuyler County, MO 14%
- Monroe County, MO 14%
- Mercer County, MO 14%
- Audrain County, MO 14%
- Grundy County, MO 12%
- Clinton County, MO 11%
- Ringgold County, IA 10%
- Putnam County, MO 9%
- Lucas County, IA 9%
- Davis County, IA 9%
- Shelby County, MO 9%
- Ralls County, MO 8%
- Appanoose County, IA 8%
- Lewis County, MO 8%
- Decatur County, IA 8%
- Pike County, MO 5%
- Gentry County, MO 4%
Sources
Shares and properties: USDA NRCS SSURGO via Soil Data Access, weighted by each component's share of its map units. Description: the USDA NRCS series description. How we count.