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

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

In short: Summit is a very deep clay soil of northeastern Oklahoma, including the Tulsa area, that formed from Pennsylvanian shale. Its subsoil is 40 to 70 percent clay of the smectite family, its official description lists a coefficient of linear extensibility (COLE) of 0.09 or more, and it holds a perched water table through winter and spring. These traits make seasonal foundation movement a central concern on Summit lots.

Where does Summit soil occur?

The USDA Natural Resources Conservation Service (NRCS) keeps an Official Series Description (OSD) for every named soil. The Summit OSD lists the series in Major Land Resource Areas 112 and 116 across eastern Oklahoma, southeastern Kansas, southwestern Missouri and northwestern Arkansas, and calls it extensive ¹. Its type location is in Rogers County, Oklahoma ¹.

Summit forms on interfluves (the broad ground between drainages), divides and hillslopes on plains, on slopes of 0 to 12 percent ¹. It developed in clayey colluvium or residuum weathered from Pennsylvanian shales ¹, which places it in the Tulsa Metro and the Northeast. Native vegetation is tallgrass prairie ¹.

What are the key properties of Summit soil?

"Smectitic" means the clay is dominated by smectite, the clay mineral group that swells most when wet ⁶. "Vertic" in the name signals soil that cracks deeply and shows slickensides, the polished shear faces left by repeated swelling, and the OSD records slickensides in the B horizons ¹.

What do these properties mean for foundations?

Very high shrink-swell

The coefficient of linear extensibility (COLE) is the change in length of a soil clod from moist to dry, and as a percent it is called linear extensibility (LEP) ³. NRCS rates 6 to 9 percent as high and more than 9 percent as very high, and notes that soils above 3 percent can damage buildings and roads and commonly need special design ⁴. Summit's COLE of 0.09 or more (9 percent or more) puts it at the high to very high end of that scale ¹⁴. The rated value for each mapped Summit unit is listed in Web Soil Survey ².

Clay soils swell when they gain water and shrink when they lose it, and localized moisture changes around a house are more damaging than uniform ones ⁵. Expansive clays are easy to spot in dry seasons by their deep cracks, and seasonal moisture change can reach from 3 to 40 feet deep depending on climate ⁶. Typical movement patterns on soils like this include perimeter drying settlement, center heave and tree-root drying.

The Oklahoma Geological Survey notes that clay-rich shales and soils weathered from shale can contain montmorillonite, a smectite clay, and that saturation from rain, lawn watering or sewer leaks can damage foundations ⁷.

Perched water

A perched water table is a temporary saturated zone that sits on top of a slow-draining layer. On Summit it sits 12 to 36 inches down from November to May in normal years ¹. Wet crawl spaces and water pressure on basement walls are related concerns; see groundwater and perched water and lateral earth and hydrostatic pressure.

Keeping moisture even

The ASCE homeowner guide stresses even soil moisture around the whole foundation, grading at least 3 inches of fall over 5 feet, downspouts discharging at least 3 feet out, and planting trees farther from the house than their mature height ⁵.

Related

• Shrink-swell and the active zone
• Soil series in the Tulsa metro
• Clay mineralogy
• Dennis soil
• Okemah soil
• Soil Series Index