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

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

In short: Grant is a deep, well-drained soil of north-central Oklahoma that formed from Permian siltstone or silty shale, sometimes under a thin cap of wind-blown silt. Its subsoil is silty clay loam with about 22 to 28 percent clay, and weathered rock starts 40 to 60 inches down. Moderate clay, water management and the depth of the siltstone are the main soil factors for foundations.

Where does Grant soil occur?

The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) places Grant in Oklahoma and south-central Kansas, in Major Land Resource Area 80A, the Central Rolling Red Prairies, at 700 to 1,500 feet elevation ¹. It is a series of large extent ¹. The type location is in Garfield County about 2 miles north and 6.5 miles west of Hillsdale, and the series was established in Grant County ¹.

Grant forms on paleoterraces, on summits and backslopes, with slopes of 0 to 20 percent ¹. Its parent material is weathered siltstone or silty shale, and some areas have a thin loess mantle ¹. That is the landscape of the North-Central (Red Prairies and Wheat Belt) region; the OSD dates the siltstone and silty shale to the Permian ¹. Permian shales of central Oklahoma are covered on the Hennessey Shale page.

What are the key properties of Grant soil?

"Fine-silty" means the soil is dominated by silt with a moderate amount of clay. "Paleoterraces" are old, high stream terraces left behind as rivers cut down. Grant is mostly cropland for wheat and other small grains, with some native tall and mid grasses ¹.

What do these properties mean for foundations?

Moderate clay

Clay soils swell when wet and shrink when dry, and uneven moisture causes more damage than uniform changes ⁴. Grant's subsoil holds about 22 to 28 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 Grant map unit is in Web Soil Survey ². For lab tests that measure swell directly, see soil testing and lab values.

Thin loess mantle

Some Grant areas carry a thin cap of loess ¹. Wind-deposited soils such as loess are among the deposits that can be collapsible, meaning they lose volume when wetted under load ⁵. Collapse depends on a loose, open structure held by weak bonds that water can weaken ⁵. The OSD does not rate collapse potential for Grant; see hydrocollapse (collapsible soil) and collapsible and loess soils.

Water and leaks

Water from leaking pipes, irrigation and redirected rainwater are common wetting sources ⁵, and sewer or water line leaks can cause localized foundation movement ⁴. The ASCE guide describes sloping soil away from the foundation and discharging downspouts away from the house ⁴. Related: erosion, undermining and washout voids and surface drainage and grading.

How do you check a specific lot?

• Look up the map unit and LEP in Web Soil Survey ².
• Keep soil moisture around the foundation even and have plumbing leaks located and repaired ⁴.
• Track existing cracks and check drainage around the house each year ⁴.

Related

• Kingfisher soil
• Hennessey Shale (Group)
• Collapsible and Loess Soils
• Fill Consolidation Settlement
• Soil Series Index