What is Nixa soil and how does it affect Oklahoma foundations?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Nixa is a very gravelly soil of the Ozark Highlands that reaches into northeast Oklahoma. It is packed with chert (flint-like rock) fragments and has a dense, brittle fragipan starting 14 to 27 inches down that slows water to a crawl. For foundations, the main issues are water perching on that dense layer, fast runoff on slopes, and a mix of rock and clay at depth.

What is Nixa soil?

Nixa is an official USDA soil series classified as "Loamy-skeletal, siliceous, active, mesic Glossic Fragiudults" ¹. "Loamy-skeletal" reflects its high rock-fragment content, and "Fragi" refers to its fragipan ¹.

It formed in colluvium (material moved downslope) and loamy residuum weathered from cherty limestone, on upland ridgetops and side slopes of the Ozark Highlands (MLRA 116A) ¹. Slopes range from 1 to 35 percent ¹. The series is mapped in Arkansas, Kansas, Kentucky, Missouri, Oklahoma, Tennessee and Virginia and is described as of large extent ¹. It was established in Christian County, Missouri, in 1942; the type location is in Marion County, Arkansas ¹. Native forests were mainly oaks and hickory ¹.

In Oklahoma, this places Nixa in the Northeast (Ozark Plateau and Grand Lake) region on Mississippian cherty limestone.

What does a Nixa soil profile look like?

Source for the table: ¹. Other properties from the official description ¹:

• Fragipan: begins at 14 to 27 inches across the series ¹.
• Deep subsoil: the fine earth in the 3Bt is clay, silty clay or silty clay loam ¹.
• Drainage: moderately well drained; permeability very slow; saturated hydraulic conductivity low ¹.
• Runoff: high to very high ¹.
• Depth to bedrock: 60 to more than 80 inches ¹.

What does Nixa soil mean for foundations?

A dense layer that holds water up

Fragic soil material is firm and brittle when moist, is not cemented (dry pieces break apart in water) and restricts roots ³. Nixa's fragipan is part of why its permeability is very slow ¹. When a saturated layer sits above unsaturated layers, soil scientists call it episaturation, the condition behind a perched water table ³. For how perched water affects basements and crawl spaces, see groundwater and perched water and crawl space moisture and wood decay.

Runoff on slopes

Nixa has high to very high surface runoff and slopes up to 35 percent ¹. The ASCE Geo-Institute homeowner guide identifies roof runoff, poor grading and shallow seepage as moisture sources to control around shallow foundations, and describes an upslope trench drain with a water barrier as one response to shallow seepage ⁴. See surface drainage and grading and erosion, creeks and slopes.

Rock fragments and clay at depth

With 35 to 85 percent chert in the subsoil ¹, digging in Nixa means working through chert gravel and cobbles. The deepest layer has clayey fine earth between the chert ¹. The official description gives no shrink-swell value; Web Soil Survey lists properties for each mapped unit ².

Where a sloping lot was leveled with fill, see fill consolidation settlement. For how water can carry soil from beneath footings, see erosion, undermining and washout voids.

How do you confirm the soil at a property?

Web Soil Survey covers more than 95 percent of U.S. counties and can produce custom soil reports ².

Related

• Pier and beam crawl space
• Water at cove joint or efflorescence
• Basements
• Oklahoma geologic provinces
• Soil series index