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

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

In short: Clarksville is a deep, gravelly soil of the Ozarks that forms on steep side slopes and narrow ridgetops, including in northeastern Oklahoma. Its upper layers are loaded with chert gravel and drain quickly, while clayey layers with more than 40 percent clay begin 3 to 4.5 feet down. Slope, runoff and the rocky, variable profile are the main foundation-related traits.

Where does Clarksville soil occur?

The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) maps Clarksville across the Ozark region (Major Land Resource Areas 116A and 116B) of Kansas, Missouri, Oklahoma and Arkansas, as well as in dissected cherty areas of other southeastern states ¹. It is a series of large extent; its type location is in Shannon County, Missouri ¹.

In Oklahoma, this places Clarksville in the Northeast (Ozark Plateau and Grand Lake) region, where the bedrock includes Mississippian cherty limestone. The soil forms in hillslope sediments over clayey residuum weathered from cherty dolomite or cherty limestone ¹. "Residuum" is material that weathered in place from the rock beneath.

What are its key properties?

"Loamy-skeletal" means the soil has a large share of rock fragments mixed into a loamy matrix. Clarksville land is mostly second-growth timber of oak, hickory and shortleaf pine, with some pasture and hayland ¹.

What is the Clarksville profile, layer by layer?

The OSD's typical profile shows how much chert the soil holds ¹:

• Surface (A): gravelly silt loam with about 30 percent chert gravel.
• Upper subsoil (Bt1 to Bt2): gravelly silt loam to very gravelly loam, 20 to 45 percent chert gravel.
• Middle subsoil (2Bt3 to 2Bt4): extremely to very gravelly clay loam, 40 to 55 percent chert gravel plus cobbles.
• Lower subsoil (3Bt5): cobbly clay.

What do the properties mean for foundations?

Steep ground and fast runoff

Clarksville occupies slopes up to 70 percent and sheds water with medium to very high runoff ¹. On sloped sites, concentrated runoff and erosion are the main soil-related concerns; see erosion, creeks and slopes, slope creep and lateral movement and surface drainage and grading. The ASCE homeowner guide describes grading soil away from a foundation and sending downspout water away from the house to keep moisture even ⁴.

Rocky upper layers, clay below

The gravelly upper layers drain readily, but the clayey residuum with over 40 percent clay begins 36 to 54 inches down ¹. Clay soils swell when wet and shrink when dry ⁴. NRCS rates shrink-swell by linear extensibility percent (LEP): under 3 percent low, 3 to 6 percent moderate, 6 to 9 percent high and 9 percent or more very high ³. The rated LEP for each Clarksville map unit is published in Web Soil Survey ².

Cut-and-fill pads

Where a building pad was cut into the hillside or built up with fill, that fill is not part of the native profile the OSD describes ¹, and its behavior depends on how it was placed; see fill consolidation settlement.

How is a specific lot checked?

• Look up the map unit, slope class and LEP in Web Soil Survey ².
• Check drainage within several feet of the foundation each year and monitor existing cracks ⁴.

Related

• Mississippian Cherty Limestone
• Northeast Oklahoma (Ozark Plateau and Grand Lake)
• Slope and Erosion Stabilization
• Hector soil
• Soil Series Index