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How do Tulsa-area sandstone ridges affect Oklahoma foundations?

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

In short: Pennsylvanian sandstone forms the ridges, hills and ledges of the Tulsa area and much of eastern Oklahoma. It weathers into loamy, well-drained soils that are often only inches to a few feet deep over rock. Lots on this ground deal more with slopes, fill, erosion and uneven rock than with clay swell.

What is Pennsylvanian sandstone?

In northeastern Oklahoma, sandstone beds alternate with shale. In Tulsa County, for example, the Coffeyville Formation was described as five zones, two of sandstone and three of shale, as much as 440 feet thick in all 5. Sandstone soils such as Collinsville and Coweta occupy ridges, interfluves and hillslopes 12. See Pennsylvanian shales for the clay soils between the ridges.

What soils form on sandstone?

Series Rock contact Depth to rock Drainage Slopes
Collinsville Hard (lithic) 4–20 in; 9 in typical 1 Well to somewhat excessively drained 1 1–35% 1
Coweta Soft (paralithic) 10–20 in; about 15 in typical 2 Well to somewhat excessively drained 2 1–30% 2
Bates Soft (paralithic) 20–40 in 3 Well drained 3 1–8% 3
Hector Hard (lithic) 14–20 in; about 15 in typical 4 Well drained 4 2–60% 4

A lithic contact is hard bedrock; a paralithic contact is soft, weathered rock.

How does rock in the soil survey compare to pier depth?

A soil series description covers the soil and the top of the rock, not what lies deeper. Coweta's description shows why that can mislead: soft sandstone at about 15 inches can be followed by hard sandstone farther down, and both are interbedded with shale 2. In 2025 installation records from Tulsa, steel push piers reached refusal at a median depth of about 12 feet, with most exterior piers between about 8 and 16 feet, including at sites where the survey showed rock within the top 40 inches 7. Survey rock depth and pier depth are therefore different measurements. See steel push piers and depth to rock from borings.

What does this mean for foundations?

Hillside lots and fill

Slopes up to 30 to 60 percent on Collinsville, Coweta and Hector soils 124 mean many lots are cut and filled to make a level pad. Fill that was not compacted can settle over time. See fill consolidation settlement and fill soils and lot history.

Slope creep

Soil on steep slopes can move slowly downhill, pulling at the downhill side of a house. See slope creep and lateral movement.

Erosion and washouts

Coweta has medium to very high runoff potential 2, and Bates has saturated hydraulic conductivity in the moderately high to high range 3, so water moves quickly over and through these soils. Leaks and concentrated roof water can carry soil away from footings. The ASCE homeowner guide recommends downspouts discharge at least 3 feet from the foundation 6. See erosion, undermining and washout voids.

Free, plain-English answers. It asks a few questions and walks you to the repair that fits.

Common questions

Which soils form on Pennsylvanian sandstone?

Common ones in eastern Oklahoma include Collinsville, Coweta and Bates. They are loamy, well drained and often shallow to sandstone.

How shallow is the rock?

Collinsville reaches hard rock at 4 to 20 inches, Coweta reaches soft sandstone at 10 to 20 inches, and Bates reaches soft sandstone or shale at 20 to 40 inches.

If rock is that shallow, why do piers sometimes go much deeper?

Sandstone often occurs as ledges with shale between them. Field records from Tulsa show steel piers stopping at a median of about 12 feet even where soil surveys show rock within a few feet, because a soil description covers only the soil and the top of the rock; soft sandstone can be followed by harder sandstone deeper down, interbedded with shale.

Do sandstone soils swell?

They are loamy rather than clayey, so seasonal swell is generally lower than on shale clays. Erosion, slope movement and fill are more common concerns.

Sources

  1. Official Soil Series Description: COLLINSVILLE Series USDA Natural Resources Conservation Service
  2. Official Soil Series Description: COWETA Series USDA Natural Resources Conservation Service
  3. Official Soil Series Description: BATES Series USDA Natural Resources Conservation Service
  4. Official Soil Series Description: HECTOR Series USDA Natural Resources Conservation Service
  5. Geolex unit references: Coffeyville USGS National Geologic Map Database (Geolex)
  6. Living With Shrink/Swell Soils: A Homeowners' Guide to Maintenance of Shallow Foundations American Society of Civil Engineers, Geo-Institute
  7. Oklahoma steel push pier installation records, 2025 (unpublished field data) TerraBrain field data

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