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

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

In short: Darnell is a shallow, sandy soil on the hills of Oklahoma's Cross Timbers, resting on Permian sandstone only 10 to 20 inches down. It drains rapidly and is not a clay soil. For houses on Darnell, the shallow rock, slopes and handling of runoff and leaks matter more than seasonal clay swelling.

Where does Darnell soil occur?

The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) lists Darnell in Oklahoma, Kansas and Texas within Major Land Resource Area 84A, the Cross Timbers ¹. It is an extensive series found at 740 to 1,315 feet elevation ¹. The type location is about 8 miles west of Tryon in Lincoln County, and the series was established in Okfuskee County in 1942 ¹.

Darnell forms on very gently sloping to steep ridge crests and upper side slopes of hills, on slopes of 1 to 45 percent ¹. It weathered from Permian sandstone ¹; Oklahoma's Permian sandstones are covered on the Garber Sandstone page, and the type location in Lincoln County lies east of the OKC metro.

What are its key properties?

A "paralithic contact" is the boundary with rock that is weathered or only weakly cemented, as opposed to hard rock. The OSD notes that the Cr sandstone has high or very high excavation difficulty, meaning it is hard to dig ¹. Darnell is used mainly as rangeland under post oak, blackjack oak and eastern red cedar ¹.

What do the properties mean for foundations?

Sandy texture, little clay

Clay soils swell when they take on water and shrink when they dry, moving foundations up and down ⁴. Darnell's surface and subsoil are sandy loam or fine sandy loam ¹. NRCS classes linear extensibility (LEP) under 3 percent as low and 3 to 6 percent as moderate ³; the rated LEP for each Darnell map unit is in Web Soil Survey ².

Rock within 20 inches

Sandstone lies 10 to 20 inches below the surface ¹. Questions about whether a foundation bears on soil, weathered rock or sound rock are covered in shale weathering and bearing strata and depth to rock from borings.

Runoff, leaks and erosion

Darnell's very high permeability and steep slopes mean water moves quickly through and across it ¹. Uneven moisture causes more damage than uniform moisture, and water or sewer leaks can produce localized movement ⁴. See erosion, undermining and washout voids and plumbing leaks under slab.

Trees

Native vegetation on Darnell is post oak, blackjack oak and eastern red cedar ¹. Tree roots can dry soil unevenly near a foundation, and the ASCE guide describes planting trees farther from the house than their mature height ⁴; see trees and roots.

How is a specific lot checked?

• Look up the map unit, slope and depth to bedrock in Web Soil Survey ².
• Grade soil to drain away from the foundation and discharge downspouts away from the house ⁴.
• Monitor existing cracks and inspect drainage around the house each year ⁴.

Related

• Garber Sandstone
• Chickasha soil
• Dougherty soil
• Fill Consolidation Settlement
• Soil Series Index