How deep is bedrock in Tulsa and Oklahoma City?
In short: Public geotechnical borings show rock at roughly 9 to 15 feet under upland shale in Tulsa, which lines up with typical steel pier depths there. Oklahoma City is more variable: Hennessey shale can sit 2 to 41 feet down, and Garber sandstone in the Edmond area was 20 to 95 feet down. Creek bottoms and river banks are the deep cases in both metros.
What do these boring numbers mean?
A boring is a test hole drilled by a geotechnical engineer to log soil and rock. These reports separate two depths:
- Weathered rock: the top of shale, sandstone or limestone that has broken down and is softer than the rock below. Engineers sometimes call it intermediate geomaterial.
- Competent rock: hard rock as each report defines it, usually by auger refusal (the drill can't advance), standard penetration test refusal, or a Texas Cone Penetrometer reading.
Each report draws these lines a little differently, so treat depths as close guides. For the geology behind them, see shale weathering and bearing strata.
What do Tulsa metro borings show?
East Tulsa shale (S 193rd E Ave, 31st to 41st St)
Nine borings for a sewer project found weathered rock at 1 to 8 feet and competent shale or limestone at 4 to 14.5 feet 1.
| Boring | Weathered rock (ft) | Competent rock (ft) | Water at end of drilling (ft) |
|---|---|---|---|
| B-1 | 7.5 | 9.5 | 7 1 |
| B-2 | 7 | 14.5 | not encountered 1 |
| B-3 | 7 | 9.5 | not encountered 1 |
| B-4 | 1 | 4 | not recorded 1 |
| B-6 | 8 | 9 | not encountered 1 |
| B-7 | 7 | 8.5 | not encountered 1 |
| B-8 | 7 | 8.5 | 7 1 |
| B-9 | 8 | 11 | 9.5 1 |
| B-10 | 7.5 | 14.5 | not encountered 1 |
Rock cores from B-4 tested at 4,880 to 9,560 psi in unconfined compression, and the report expected that a pneumatic hammer or blasting would be needed to excavate 1.
South Tulsa, 91st St between Memorial and Mingo
Five borings for one retaining wall hit highly weathered Nowata shale at about 13.5 feet and weathered shale at about 18.5 feet, and were dry 2. Two borings for a second wall found clay all the way to 30 and 35 feet with no shale, and water at 13.5 to 15 feet 2. Clay samples had liquid limits up to 56 and plasticity index up to 39 2. See soil testing and lab values for what those numbers mean.
Central Tulsa, I-44 and US-75
Ten borings in the Holdenville unit reached competent rock at 13.5 to 14.5 feet on one wall and 18.5 to 19.5 feet on the other 3. Groundwater appeared during drilling in several holes but none was found after drilling 3.
What do Oklahoma City metro borings show?
Hennessey shale, I-35/I-240 interchange
The Hennessey unit is red clay shale and mudstone 4. Depth to bedrock varied widely across three structures:
| Structure | Depth to bedrock by boring (ft) |
|---|---|
| Retaining Wall C2 | 16, 5.5, 2, 2, 2 4 |
| Bridge D | 10.5, 15, 16, 21, 10.5 5 |
| Bridge C (under alluvium) | 35.5, 17.5, 21, 41 6 |
No groundwater was observed at Bridge D or Bridge C, while one Wall C2 boring had water at 20 feet 456. The Wall C2 report noted saturated overburden in places as shallow as 3 feet and perched water at the rock contact 4.
Garber sandstone, I-35 over Waterloo Road (north Edmond)
The Garber unit is described as red clay shales, sandy shales and cross-bedded sandstones 7. Eight borings found competent rock far deeper than in Tulsa 7.
| Borings | Top of weathered rock (ft) | Top of competent rock (ft) |
|---|---|---|
| A-1 to A-4 | 40, 60, 90, 85 | 41.5, 60.5, 95, 85 7 |
| B-1 to B-4 | 20, 60, 76, 91.5 | 20.5, 60.5, 85, 91.5 7 |
Water levels after drilling were mostly 30 to 35 feet, and the report notes they change with the seasons 7.
What do the summary statistics show?
Calculated from the borings above (drilled borings that reached rock, each counted once):
| Group | Borings | Median (ft) | Range (ft) |
|---|---|---|---|
| Tulsa, competent rock, all groups | 19 | 13.5 to 14.5 | 4 to 19.5 13 |
| East Tulsa shale only | 9 | 9.5 | 4 to 14.5 1 |
| OKC Hennessey, top of bedrock | 14 | 15.5 | 2 to 41 456 |
| OKC Garber, competent rock | 8 | about 73 | 20.5 to 95 7 |
How do rock depths compare with pier depths?
Oklahoma steel push pier installation records show typical pier depths of 8 to 16 feet, with a median of about 12 feet in Tulsa 8. That sits close to the Tulsa boring medians above 13. A steel push pier is driven until it meets enough resistance to carry the house, which can be rock or dense soil.
Where borings found clay to 30 and 35 feet with no rock, as on the second 91st St wall 2, or rock 20.5 to 95 feet down, as at the Garber site 7, a pier may stop on friction in dense soil before reaching rock. For a city-by-city overview, see bedrock in the Tulsa metro and bedrock in the OKC metro.
What are the limits of this data?
- Highway and sewer borings are often on low ground, cuts or fill, so a hilltop lot may be shallower.
- Reports sometimes conflict between their summary tables and boring logs; the original PDF is the authority.
- Rock depth can change sharply over short distances, as the Bridge C borings show 6.
Related
- Depth to rock from borings
- Bedrock - Tulsa metro
- Bedrock - OKC metro
- Hennessey shale
- Garber sandstone
- Loads, pier spacing and capacity
Common questions
How deep is rock under Tulsa?
In public drilled borings on upland shale in Tulsa reviewed here, competent rock was found at a median of about 14 feet, with most between about 9.5 and 14.5 feet. Two borings for one retaining wall went 30 and 35 feet without reaching rock.
How deep is rock in Oklahoma City?
It varies with the bedrock unit. Borings in Hennessey shale at the I-35/I-240 interchange hit bedrock between 2 and 41 feet, while borings in Garber sandstone at I-35 and Waterloo Road reached competent rock at 20.5 to 95 feet.
How deep do steel push piers go in Tulsa?
Oklahoma installation records show typical pier depths of about 8 to 16 feet, with a median near 12 feet in Tulsa, which is close to the depth of weathered and competent shale in nearby borings.
Why do borings close together show different rock depths?
Bedrock surfaces are uneven, and alluvium (creek-deposited soil) fills old channels. One Oklahoma City bridge site had bedrock at 17.5 feet in one boring and 41 feet in another.
Sources
- 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, Retaining Walls A and B Along 91st Street South from South Memorial Drive to South Mingo Road City of Tulsa
- Geotechnical Engineering Report, I-44/US-75 Interchange Reconstruction, Retaining Walls RW-21 & RW-22 Oklahoma Department of Transportation
- Report of Geotechnical Engineering Services, Proposed Retaining Wall C2, Crossroads Interchange Reconstruction, I-35/I-240 Oklahoma Department of Transportation
- Report of Geotechnical Engineering Services, Crossroads Interchange Reconstruction, Bridge D, I-35/I-240 Interchange Oklahoma Department of Transportation
- Geotechnical Engineering Services Report, Crossroads Interchange Reconstruction, Bridge C, I-35/I-240 Interchange Oklahoma Department of Transportation
- Geotechnical Engineering Report, Three Span Bridge, Interstate 35 over Waterloo Road Oklahoma Department of Transportation
- Oklahoma steel push pier installation records, 2025 (unpublished field data) TerraBrain field data
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