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

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

In short: Foard is a clay soil of southwest Oklahoma that formed in old alluvium from the Wichita Mountains over Permian red beds. Its subsoil holds 35 to 45 percent smectitic clay, shows slickensides from shrink-swell, and is affected by sodium, which is linked to very slow water movement. Seasonal clay movement and very slow drainage are the main soil traits behind foundation problems on Foard.

Where does Foard soil occur?

The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) places Foard in Oklahoma and Texas, in Major Land Resource Areas 78B and 78C, the Central Rolling Red Plains ¹. It is an extensive series ¹. The type location is in Cotton County, Oklahoma, at 1,092 feet elevation, and the series was established in Foard County, Texas ¹.

Foard forms on nearly level to gently sloping broad summits and shoulders of terrace pediments, on slopes of 0 to 5 percent ¹. Its parent material is clayey old alluvium from granitic outwash of the Wichita Mountains, over clayey Permian red beds ¹. That places it in the Southwest (Lawton and Red Plains) region.

What are its key properties?

"Natrustolls" are prairie soils with a natric horizon, a clay subsoil high in sodium. "Slickensides" are polished, grooved surfaces found in shrink-swell clays ⁵. Foard is used mainly for small grains and cotton, with some native range ¹.

What do the properties mean for foundations?

Vertic shrink-swell

The "Vertic" part of Foard's name means it meets shrink-swell criteria close to those of the Vertisols: cracks at least 5 mm wide through 30 cm or more within 125 cm of the surface plus a slickenside layer, or a linear extensibility of 6.0 or more to 100 cm ¹. Vertisols shrink as they dry, swell as they rewet and cause serious engineering problems, including damage to structures ⁵. NRCS classes linear extensibility (LEP) of 6 to 9 percent as high and 9 percent or more as very high ³; the LEP for each Foard map unit is published in Web Soil Survey ².

Sodium

Exchangeable sodium percentage (ESP) in Foard rises from under 15 in the upper subsoil to 15 to 25 in deeper layers ¹. Soil structure starts to break down once about 15 percent of the exchange sites hold sodium ⁶. Sodium makes clay particles repel each other and stay dispersed; dispersed clay plugs pores, forms crusts and restricts movement of air and water ⁶. That is consistent with Foard's very slow permeability ¹.

Typical movement patterns

Clay soils heave when they gain moisture and settle when they dry, and uneven moisture causes more damage than uniform moisture ⁴. Related movement patterns:

• Perimeter drying settlement in dry spells.
• Perimeter wetting heave after rain.
• Center heave under slabs.
• Tree-root desiccation settlement near trees.

What practical points apply to a Foard lot?

• Look up the map unit and LEP in Web Soil Survey ².
• Keep soil moisture around the foundation as even as practical, watering more on the drier south and west sides in drought ⁴.
• Grade soil away from the house and repair leaks quickly ⁴.

Related

• Hollister soil
• Shrink-Swell and Active Zone
• Soil Testing and Lab Values
• Wichita Granite and Granite Wash
• Soil Series Index