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

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

In short: Verdigris is a very deep, well-drained silty soil that forms on stream flood plains in northeastern Oklahoma, including the Tulsa area. It has a thick, dark silty topsoil and averages 15 to 33 percent clay, but its official description states that it is subject to flooding. For buildings on Verdigris, flood exposure and soft, water-laid layers are the main foundation considerations.

Where does Verdigris soil occur?

The USDA Natural Resources Conservation Service (NRCS) maintains an Official Series Description (OSD) for each named soil. The Verdigris OSD lists the series in Major Land Resource Areas 76, 112, 116 and 118 and LRU 84A, across southeastern Kansas, northeastern Oklahoma and southwestern Missouri, and calls it extensive ¹. Its type location is on the flood plain west of the Verdigris River near Elk City, Kansas ¹.

Verdigris forms on flood plains with 0 to 3 percent slopes, in silty alluvium (sediment laid down by streams) ¹. That ties it to the Quaternary alluvium along streams in the Tulsa Metro and the Northeast. Most Verdigris land is cultivated for corn, sorghum, alfalfa and wheat ¹.

What are its key properties?

"Cumulic" is a soil-taxonomy term for an unusually thick dark topsoil, which on flood plains typically builds up as floods add sediment. Below 40 inches, textures range from sandy loam to silty clay ¹.

Wynona is a closely related flood-plain soil that is somewhat poorly drained, and Osage is an associated clayey bottomland soil with high shrink-swell ¹².

What do the properties mean for foundations?

Flood exposure

The OSD states plainly that Verdigris soils are subject to flooding, though it does not give a frequency ¹. Official flood hazard maps for a specific address are published through FEMA's Flood Map Service Center ⁵. The Oklahoma Geological Survey notes that Oklahoma floods tend to occur in spring and fall, and that flood-prone areas are mapped to show land with about a 1-in-100 chance of flooding in a given year ⁶. See creeks and flood history.

Soft, layered sediment

Verdigris formed in stream-laid silty alluvium, and its textures below 40 inches range from sandy loam to silty clay ¹. Layered alluvium is the setting for soft soil consolidation, where wet, compressible layers settle under load. Where a lot was raised with placed soil, fill consolidation settlement is a separate factor.

Shrink-swell and water

NRCS rates shrink-swell by linear extensibility: under 3 percent is low and 3 to 6 percent moderate ⁴. Verdigris has a fine-silty control section with 15 to 33 percent clay, while neighboring Osage has a clayey (fine) control section and high shrink-swell ¹². The rated value is in Web Soil Survey ³. The ASCE homeowner guide recommends at least 3 inches of fall over the first 5 feet and downspouts that discharge at least 3 feet from the foundation ⁷.

Related

• Wynona soil
• Osage soil
• Erosion, creeks and slopes
• Soil series in the Tulsa metro
• Soil Series Index