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

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

In short: Coweta is a shallow, loamy soil on eastern Oklahoma ridges and hillslopes that rests on soft Pennsylvanian sandstone, interbedded with shale, just 10 to 20 inches down. It holds about 10 to 30 percent clay and drains well. Shallow, soft rock and runoff on sloping ground are its main foundation-related traits.

Where does Coweta soil occur?

The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) places Coweta in Major Land Resource Areas 84A, 112, 117 and 118 in eastern Oklahoma, and possibly southeastern Kansas and southwestern Missouri ¹. The type location is in Wagoner County about 11 miles northeast of the town of Coweta, and the series is of moderate extent ¹.

Coweta forms on broad, smooth upland ridges, interfluves and hillslopes, on slopes of 1 to 30 percent ¹. It weathered from sandstone interbedded with shale of Pennsylvanian age ¹; see Pennsylvanian sandstones and Pennsylvanian shales. This is common ground in the Tulsa metro and East-Central (Arkoma) region.

What are Coweta soil's key properties?

A "Bw" horizon is a subsoil layer that has changed color or structure but has not gained much clay. Coweta land is mainly rangeland of tallgrass prairie, with tame pasture on slopes under 15 percent and small cultivated areas on slopes under 5 percent ¹.

What does Coweta soil mean for foundations?

Low clay content

Clay soils swell when wet and shrink when dry, which is the main driver of seasonal foundation movement ⁴. Coweta's subsoil has 10 to 30 percent clay ¹. NRCS classes linear extensibility (LEP) under 3 percent as low, 3 to 6 percent as moderate, 6 to 9 percent as high and 9 percent or more as very high ³. The LEP for each Coweta map unit is listed in Web Soil Survey ².

Soft rock, not hard rock

The rock under Coweta is described as soft sandstone, reached at 10 to 20 inches ¹. That contrasts with the neighboring Collinsville series, which sits on hard sandstone at 4 to 20 inches ⁵. How soft, interbedded rock behaves as a bearing layer is covered in shale weathering and bearing strata. In Oklahoma steel push pier records, piers typically reached 8 to 16 feet, with a median near 12 feet in Tulsa ⁶; the depth to rock from borings page summarizes measured rock depths.

Runoff and erosion

Coweta sheds medium to very high runoff on slopes up to 30 percent ¹. Uneven moisture and water line or sewer leaks can cause localized movement ⁴. Related mechanisms are described under erosion, undermining and washout voids and fill consolidation settlement.

How do you check a specific lot?

• Look up the map unit, slope and depth to bedrock in Web Soil Survey ².
• Grade soil away from the foundation and discharge downspouts away from the house ⁴.
• Repair leaks quickly and confirm repairs with pressure tests ⁴.

Related

• Collinsville soil
• Soil Series - Tulsa Metro
• Bedrock - Tulsa Metro
• Steel Push Piers
• Soil Series Index