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

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

In short: Stephenville is a moderately deep, well-drained soil of central Oklahoma that formed from weathered Permian sandstone. Its subsoil is sandy clay loam or fine sandy loam, and soft sandstone typically sits 20 to 40 inches down. For houses on Stephenville, the sandy texture, the shallow rock and how water is handled around the foundation matter more than clay swelling.

Where does Stephenville soil occur?

Every named soil in the U.S. has an Official Series Description (OSD) kept by the USDA Natural Resources Conservation Service (NRCS). The Stephenville OSD places the series in central Oklahoma, in Major Land Resource Area 84A, the Northern Cross Timbers, and calls it extensive ¹. Its type location is in Oklahoma County, about 2.5 miles east and 1 mile north of Spencer ¹.

Stephenville forms on the side slopes of hills on uplands, on slopes of 1 to 25 percent ¹. That places it in parts of the OKC Metro ¹; for the local Permian sandstone, see the Garber Sandstone page. Native vegetation is post oak, blackjack oak, hickory and eastern red cedar with tall and mid grasses, the typical Cross Timbers mix ¹.

What are its key properties?

A "paralithic contact" is the top of soft, weakly cemented rock that can be dug with effort. In Stephenville it is weakly cemented sandstone ¹. The "Bt" horizon is the subsoil layer where clay has collected over time.

Closely related soils include Darnell and Darsil, which are shallower to rock and sit on hill crests, and Harrah and Konawa, which are deeper ¹.

What do the properties mean for foundations?

Shrink-swell

Clay soils swell when wet and shrink when dry, and uneven moisture change is what moves foundations ⁴. NRCS rates this with linear extensibility: under 3 percent is low, 3 to 6 percent moderate, 6 to 9 percent high, and above 9 percent very high ³. Stephenville's subsoil is sandy clay loam rather than clay, and the OSD does not record the cracking or slickensides (polished shear surfaces) that mark strongly expansive soils ¹. The rated value for any map unit can be checked in Web Soil Survey ².

Statewide, the Oklahoma Geological Survey notes that more than 75 percent of Oklahoma has bedrock that can produce expansive soils, so nearby shale-derived soils can behave very differently from Stephenville ⁵.

Shallow, soft sandstone

Because soft sandstone is only 20 to 40 inches down, footings and piers on Stephenville lots meet rock quickly ¹. Weakly cemented sandstone is not the same as hard rock, which is why the actual bearing layer is usually confirmed during repair work. See shale weathering and bearing strata and bedrock in the OKC metro.

Water, slopes and erosion

Runoff on Stephenville ranges from low on gentle slopes to high on slopes steeper than 20 percent ¹. Sandy and loamy soils on slopes are more open to erosion, undermining and washout voids when roof water or leaks are concentrated next to a foundation. The ASCE homeowner guide recommends that ground slope at least 3 inches down over the first 5 feet away from the house and that downspouts discharge at least 3 feet out ⁴.

Hillside lots are also often leveled with cut and fill, which brings in fill consolidation settlement as a separate issue from the native soil.

Related

• Soil series in the OKC metro
• Darnell soil
• Konawa soil
• Garber Sandstone
• Surface drainage and grading
• Soil Series Index