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

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

In short: Renfrow is a deep, well-drained soil formed from clayey Permian shale on low hills of north-central Oklahoma. Below about 13 inches it is clay, and its official description records seasonal cracks, slickensides and a high linear extensibility, all signs of strong shrink-swell. Houses on Renfrow are exposed to seasonal foundation movement as the clay wets and dries.

What is Renfrow soil?

Renfrow is an official USDA soil series classified as "Fine, mixed, superactive, thermic Udertic Paleustolls" ¹. "Udertic" marks a vertic intergrade, a soil trending toward the Vertisols ³. Vertisols are clay soils that crack when dry and swell when wet, a movement that creates serious engineering problems ⁴.

The soil formed in material weathered from clayey Permian shale on summits and backslopes of low hills, with slopes of 0 to 5 percent ¹. It occurs in the Central Rolling Red Prairies (MLRA 80A) of Oklahoma, Kansas and Texas and is rated as extensive ¹. The type location is in Kay County, about 4 miles south and 3 miles west of Tonkawa; the series was established in 1931 ¹. Mean annual precipitation is about 32 inches (range 26-40) ¹. Most areas are farmed to wheat ¹.

In Oklahoma, Renfrow is mapped in the North-Central (Red Prairies and Wheat Belt) and OKC Metro regions, on red-bed shales such as the Hennessey Shale and Wellington Formation.

What does a Renfrow soil profile look like?

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

• Clay: 35 to 55 percent in the control section ¹.
• Cracks: at least 5 mm wide through 30 cm or more, within 125 cm of the surface, for some time in most years ¹.
• Linear extensibility: 6.0 cm or more between the surface and 100 cm ¹.
• Saturated hydraulic conductivity: low. Runoff high to very high ¹.
• Shale: noncemented densic shale deeper than 60 inches ¹.

What does Renfrow soil mean for foundations?

Strong shrink-swell

Slickensides are polished, grooved faces formed by repeated shrinking and swelling ⁴, and Renfrow has them through most of its subsoil ¹. Its linear extensibility of 6 cm or more in the upper meter ¹ meets the key criterion soil taxonomy uses for vertic subgroups ³. On a percent basis, the USDA rates 6 to 9 percent as "high" and 9 percent or more as "very high" ⁶; the value for each mapped unit is in Web Soil Survey ².

Clayey soils heave as they gain water and settle as they dry, and uneven moisture change around a shallow foundation causes the most damage ⁵. Patterns to read about:

• Perimeter drying settlement (edge drop)
• Perimeter wetting heave (edge lift)
• Center heave
• Tree-root desiccation settlement

Moisture control

The ASCE Geo-Institute guide lists the main moisture sources to manage on shrink-swell soils ⁵:

Soil moisture at 5, 25, 60 and 75 cm is measured by the Oklahoma Mesonet, whose more than 110 stations cover all 77 counties ⁷.

Related

• Kirkland soil
• Norge soil
• Shrink-swell and the active zone
• Heave vs settlement
• Soil series in the OKC metro