Parts of Tehama County, including areas around Red Bluff, Corning, and Antelope, are sinking. — a condition that could cause damage to infrastructure and deplete groundwater permanently if the ag-producing county does not reverse it, geologists say.
For those who wonder, Redding and the rest of Shasta County aren’t having the same problem, in part because Shasta’s groundwater is replenished by the ACID Canal, flowing from the Sacramento River. It’s also because Shasta doesn’t have as much agriculture stressing the groundwater supply, according to groundwater experts in both counties’ public works departments.
Mid- to southwestern parts of Tehama County are suffering land subsidence, a drop in the Earth’s crust when too much groundwater is removed. The soil collapses into the space left by the lack of water, making the ground above it sink.
One cause is groundwater partially dried up during years of heavy drought. But the main issue in Tehama County is people are pumping too much water out of the ground in places like the Red Bluff and Corning sub-basins, said Justin Jenson, Tehama’s public works deputy director. More than 90% of that pumped-out groundwater goes to the county’s agriculture — mostly almond, walnut and pistachios orchards, Jenson said.
If Tehama County doesn’t take steps to reverse the problem, repercussions could be devastating, geologists say.
What land subsidence could do to Tehama, and what it’s done in other parts of California
Most land subsidence in California and other parts of the world is caused by humans pumping too much water out of the ground, according to U.S. Geological Survey. It’s a slow process that can take years to become a disaster — and can take as long to fix, when fixes are still possible.
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Joseph Poland with the USGS stands at what was the point of “maximum subsidence in the United States” in 1977: the San Joaquin Valley southwest of Mendota, California. The year signs on the pole show the approximate ground level in 1925, 1955 and 1977.
Subsidence compacted the ground in parts of the San Joaquin Valley, dropping ground level almost 30 feet in the 50 years between 1925 and 1977, according to USGS geologists.
Even slight shifts in ground level can cause damage to buildings and infrastructure like bridges and overpasses, Jenson said.
If left unchecked, land subsidence can permanently reduce the amount of groundwater an aquifer can hold by reducing its storage space. In worst cases, that could mean less to no groundwater for people, crops and wildlife living in the area, according to the USGS.
Worst case scenarios also include holes and fissures opening up as the dry, brittle ground collapses. This happened in the Mojave Desert near the now-dry Lucerne Lake in San Bernardino County. Geologists reported fissures more than 3 feet deep and 3 feet wide opened up as the ground crumbled and collapsed.
Loren Metzger at the USGS took this photo of one of the fissures that opened up after the withdrawal of groundwater near what was Lucerne Lake in San Bernardino County/Mojave Desert. Some fissures are more than 3.3 feet wide and deep. “Fissuring often is associated with localized differential compaction of sediments,” the USGS reported.
Why land in Redding isn’t sinking
Shasta County is spared land subsidence for a few reasons, according to Shasta’s Public Works Director Troy Bartolomei.
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First, Shasta has less agriculture pumping out groundwater.
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Second, the county’s “very large heavy aquifers” can replenish Shasta’s groundwater faster than Tehama’s.
The third reason Shasta isn’t sinking has to do with the way it irrigates valley farms south of Redding, toward the Tehama County line. Water flows from the Sacramento River via the ACID (Anderson Cottonwood Irrigation District) canal. “All that irrigation helps to charge the aquifer” and keep it healthy, Bartolomei said.
The Anderson Cottonwood Irrigation District canal where it passes under Cypress Avenue in Redding. Two wet winters left the canal brimming in Redding on May 1, 2024.
More: After seeing land sinking in Red Bluff and Corning areas, Tehama County calls meeting
ACID Canal serves approximately 800 customers and irrigates approximately 7,000 acres of farmland, according to the district’s website.
Future long-term drought or increasing demand for groundwater could change that delicate balance, so Shasta County participates in a voluntary groundwater monitoring program with other California counties. “Because we have a healthy aquifer that recharges itself, we don’t need expensive monitoring by the state” like Tehama County does, Bartolomei said.
Tehama land subsidence may still be reversible
Tehama County’s sinking problem could become irreversible if people don’t make changes soon, according to Jenson.
That’s because as empty underground water channels fill with collapsed soil, the space for water sources to refill the underground reservoirs becomes smaller. Even during wet winters like 2024-25, there’s less opportunity for those water sources to recharge those aquifers fast enough to save them.
One of the areas losing groundwater the fastest is between Red Bluff and Corning, where there’s a lot of competition for water, Jenson said.
This map shows areas where California land is sinking due to land subsidence. The deeper the blue color, the more the land dropped between 2015 and 2023, according to NASA.
The good news, he said, is the problem is still likely reversible.
However, it will take long-term community action to change it. That’s because “both the cause of subsidence and the fix … take a really long time. If you don’t pre-plan to resolve the issue then you can cause a future problem that you cannot fix.” The Tehama County Board of Supervisors is trying to do just that, Jenson said.
The board announced it will host a public meeting on Tuesday, June 3 to discuss possible solutions to the county’s land subsidence problem.
Tehama had “observable land subsidence on a scale that has never been recorded,” county officials said in the announcement.
Jessica Skropanic is a features reporter for the Record Searchlight/USA Today Network. She covers science, arts, social issues and news stories. Follow her on Twitter @RS_JSkropanic and on Facebook. Join Jessica in the Get Out! Nor Cal recreation Facebook group. To support and sustain this work, please subscribe today. Thank you.
This article originally appeared on Redding Record Searchlight: Why Red Bluff, Corning are sinking but Redding in Shasta County is not
