How deep is rock under Tulsa and Oklahoma City?

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

In short: Under upland ground in Tulsa, shale or limestone is often within about 2 to 15 feet of the surface. Along creeks and the Arkansas River, clay and river deposits can run 20 to 35 feet or more before rock. South of Oklahoma City, borings in McClain County found competent shale at 15.5 to 25 feet.

Why does depth to rock matter?

Rock depth controls how deep foundation piers may go and whether they end on rock or on friction in dense soil. Bedrock here means shale, sandstone or limestone below the soil. "Weathered" rock has partly broken down; "competent" rock is hard enough that drilling stalls. For pier basics, see steel push piers, and for the full boring-by-boring tables, see borings: depth to rock in Tulsa and OKC.

What do Tulsa city reports show?

Location	Weathered rock	Competent rock	Notes
E 91st St, Memorial to Mingo (Nowata unit)	about 13.5 ft	borings stopped in weathered shale near 19 ft	Two other borings found clay to 30 and 35 ft with no shale; water at 13.5 to 15 ft ¹
S 193rd E Ave, 31st to 41st St	1 to 8 ft	4 to 14.5 ft	Rock cores 4,880 to 9,560 psi ²
E Pine St and N 71st E Ave	8.5 ft	13 to 14.5 ft	Shale with limestone; fat clay (PI 27) at 5 to 7 ft ³
S 69th to 71st E Ave, E 9th to 10th St	decomposed shale from 15 in	hand-auger refusal on shale 15 to 23 in below pavement	4 of 12 holes refused ⁴
Arkansas River corridor	shale about 5 to 10 ft below the river bottom	about 20 to 30 ft below the banks	Nellie Bly, Wewoka and Senora formations ⁵

Rock strength varies widely

Strength is reported as unconfined compressive strength (UCS), the pressure a rock core takes before it crushes.

East Tulsa (S 193rd E Ave) cores: 4,880 to 9,560 psi, and the report expected a pneumatic hammer or blasting would be needed for trenching ².
Arkansas River shale at Sand Springs averaged 565 psi over six tests, and at Jenks averaged 737 psi over nine tests ⁵.

That is more than a tenfold range between the strongest east Tulsa cores and the weakest river-valley shale ²⁵. Weak shale can soften further when wet, a topic covered in shale weathering and bearing strata.

Upland vs creek bottom

The 91st St report illustrates the pattern: one set of borings hit Nowata shale near 13.5 feet, while the other went through clay to 30 to 35 feet without finding rock and found water at 13.5 to 15 feet ¹. The Arkansas River data shows the same thing on a bigger scale, with overburden (soil above rock) 18 to 35 feet thick in the river banks versus about 4 to 10 feet within the channel at the Sand Springs and South Tulsa/Jenks sites ⁵.

In practice this means a shallow pier refusal on an upland shale site is consistent with nearby borings, while the same shallow depth near a creek or river terrace is less consistent with the boring record ¹⁵. See Quaternary alluvium and terraces for those deposits.

What do borings show in central Oklahoma?

McClain County (I-35 and SH-59)

A state maintenance and residency facility study reported competent shale (standard penetration test refusal) at 15.5 to 25 feet ⁶. Above the rock were lean to fat clays, with plasticity index up to 41, that the report classified as expansive, over very weathered shale ⁶. No groundwater was found during drilling, though high moisture in several clay samples led the report to expect water in excavations ⁶.

What soil surveys say

NRCS Official Series Descriptions record what lies beneath each soil series:

Kirkland: the typical profile reaches weakly cemented siltstone at 208 cm, about 82 inches ⁷.
Renfrow (type location in Kay County, Oklahoma): formed in material weathered from Permian clayey shale, with noncemented shale more than 60 inches down ⁸.

For more on these soils, see Kirkland and Renfrow.

What do borings show about groundwater?

Three east Tulsa borings had water at 7 to 9.5 feet at the end of drilling, and groundwater was not observed in four of the nine borings ².
The 91st St creek-side borings had water at 13.5 to 15 feet; the upland borings were dry ¹.
Water perched on top of rock is common; see groundwater and perched water.

Common questions

Is bedrock shallow in Tulsa?

On many upland sites it is. City of Tulsa reports show shale as shallow as 15 to 23 inches below pavement in one east Tulsa neighborhood and competent rock within 4 to 14.5 feet at borings for two east Tulsa utility projects.

Why is rock deeper near the Arkansas River?

River and creek deposits fill in over the shale. Along the Arkansas River in Tulsa County, shale is generally about 5 to 10 feet below the river bottom but 20 to 30 feet below the banks.

How strong is Tulsa-area shale?

It varies a lot. Rock cores from an east Tulsa sewer project tested at 4,880 to 9,560 psi, while shale along the Arkansas River averaged only 565 to 737 psi.

How deep is rock south of Oklahoma City in McClain County?

At a state facility near I-35 and SH-59, borings reached competent shale at 15.5 to 25 feet under expansive clay and very weathered shale.

Sources

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
Report for Geotechnical Drilling and Laboratory Testing Services, Proposed Jack and Bore Construction, TMUA ES 2025-09 City of Tulsa / Tulsa Metropolitan Utility Authority
Geotechnical Explorations, City of Tulsa Non-Arterial Maintenance Zone 3017 City of Tulsa
Arkansas River Corridor Projects: Existing Geotechnical Resource Review Tulsa County River Projects
Subsurface Exploration, New ODOT Maintenance and Residency Facilities Oklahoma Department of Transportation
Official Series Description - KIRKLAND Series USDA Natural Resources Conservation Service
Official Series Description - RENFROW Series USDA Natural Resources Conservation Service

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