What bedrock is under Tulsa, Oklahoma homes and how deep is it?
In short: Tulsa sits on layered Pennsylvanian-age rock, mostly gray shale with sandstone and thin limestone 124. On upland shale, public borings usually reach rock within about 4 to 20 feet 234, while river corridors have 18 to 35 feet of sand and clay on the banks 1. Tulsa steel push piers stop at a median of about 12 feet 5.
What rock layers are under Tulsa?
Engineering reports across the metro describe the same basic pattern: clay soil over shale, with sandstone and limestone layers mixed in.
| Unit named in reports | Description | Example location |
|---|---|---|
| Nowata | Clay shales and sandy shales, minor lens-shaped sandstone, a few limestones usually under 1 foot thick; about 60 ft thick near Kansas, thickening to about 200 ft near Broken Arrow 2 | 91st St S, Memorial to Mingo 2 |
| Holdenville | Mainly shale with minor sandstone, siltstone and limestone, about 50 to 180 ft thick 4 | I-44/US-75 interchange 4 |
| Nellie Bly, Wewoka, Senora | Predominantly gray, thinly bedded shale, weathered and fractured in zones 1 | Arkansas River corridor 1 |
| Unnamed shale and limestone | Dark gray to gray shale and limestone, extremely weak to strong 3 | East Tulsa, Spunky Creek 3 |
Formation names change across the metro, so the map for a specific quadrangle is the reference for any one address. See Pennsylvanian shales and Pennsylvanian sandstones.
How deep is rock in public borings?
| Setting | Finding |
|---|---|
| East Tulsa shale and limestone | Weathered rock at 1 to 8 ft; competent rock at 4 to 14.5 ft in nine borings 3 |
| South Tulsa, 91st St (Nowata) | Weathered shale at about 13.5 ft along one wall; lean clay with no shale found along the other 2 |
| I-44/US-75 (Holdenville) | Competent rock at about 13.5 to 19.5 ft 4 |
| Arkansas River channel | Rock about 5 to 10 ft down 1 |
| Arkansas River banks | 18 to 35 ft of alluvium over shale 1 |
At I-44/US-75, one boring hit a well-cemented sandstone layer near the surface with a significant thickness of sandy lean clay beneath it, and the report said it should not be considered competent rock 4. A hard layer near the surface is not always the bottom.
What is under Tulsa's river corridors?
Alluvium is sediment laid down by rivers. Along the Arkansas River it is mostly poorly graded sand to silty sand with infrequent clay seams and low gravel content, very loose to loose, with clay layers that are very soft to soft 1. Groundwater on the banks is presumed to be near the river level 1. See Quaternary alluvium and terraces.
What clay sits on top of the rock?
The soil over Tulsa shale can be highly plastic. Lab tests on the 91st Street walls found fat clay with plasticity indices up to about 39 2, and east Tulsa samples ranged from 23 to 34 3. Plasticity index is a lab measure of how much water a clay can take on while staying moldable; building codes treat a value of 15 or more as one sign of expansive soil 7 (see soil testing and lab values). Statewide, more than 75% of Oklahoma contains bedrock units that can serve as sources for expansive soils 6.
How does water behave on the shale?
Five of nine east Tulsa borings recorded water at some point, at depths from 3.5 to 18.5 feet, with end-of-drilling readings of 7 to 9.5 feet; the others were dry 3. The 91st Street report found water at 13.5 to 15 feet along one wall and dry borings along the other 2. Water held on top of tight rock or clay is called perched water. See groundwater and perched water.
How deep do Tulsa piers go?
On one large Tulsa site, 396 logged steel push piers refused at a median of 12 feet, with the middle half between 9 and 14 feet and a range of 2 to 40 feet, at a median pressure of about 9,000 psi 5. Depth varied by building: one phase had a median of 15 feet, another 10 feet, and one building ran 17 to 40 feet 5. A single building's depths are not a reliable guide for an entire site.
Related
- Soil series in the Tulsa metro
- Tulsa metro region
- Depth to rock in Tulsa and OKC
- Shale weathering and bearing strata
- Steel push piers
Common questions
What kind of rock is under Tulsa?
Mostly gray shale of Pennsylvanian age, with sandstone and thin limestone layers. Engineering reports in the metro name units such as the Nowata, Holdenville, Nellie Bly, Wewoka and Senora.
How deep is rock in Tulsa?
Public borings on upland shale commonly reached weathered or competent rock between about 4 and 20 feet, while borings on Arkansas River banks found 18 to 35 feet of river sand and clay over the shale.
How deep do foundation piers go in Tulsa?
On one large Tulsa site with nearly 400 logged steel push piers, the median refusal depth was 12 feet, with half of piers between 9 and 14 feet and a full range of 2 to 40 feet.
Why do Tulsa crawl spaces and yards stay wet after rain?
Water often sits on top of tight shale or clay layers as perched water; Tulsa borings that found water commonly found it at shallow depths above or near the rock.
Sources
- Existing Geotechnical Resource Review Technical Memorandum (Arkansas River Corridor Projects, Appendix Q) Tulsa County River Projects
- Geotechnical Engineering Report, Retaining Walls A and B Along 91st Street South from South Memorial Drive to South Mingo Road City of Tulsa
- Report for Subsurface Investigation and Laboratory Testing Services, TMUA Spunky Creek MS South Phase 3 City of Tulsa / Tulsa Metropolitan Utility Authority
- Geotechnical Engineering Report, I-44/US-75 Interchange Reconstruction, Retaining Walls RW-21 & RW-22 Oklahoma Department of Transportation
- Oklahoma steel push pier installation records, 2025 (unpublished field data) TerraBrain field data
- Geologic Hazards in Oklahoma Geological Society of America (abstract by K. V. Luza, Oklahoma Geological Survey)
- Seattle Residential Code 2018, Chapter 4 Foundations (IRC-based text of R403.1.8.1) City of Seattle Department of Construction and Inspections
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