Ground subsidence in the San Joaquin Valley
The San Joaquin Valley holds some of the largest documented land subsidence on Earth — historically up to about 9 meters near Mendota — caused by agricultural groundwater pumping. USGS and NASA measured renewed rapid subsidence during recent droughts. California's SGMA now obliges groundwater sustainability agencies to monitor and address it.
What is documented here
The San Joaquin Valley holds the textbook example of groundwater-driven land subsidence. By the 1970s, parts of the valley near Mendota sank roughly nine meters — among the largest elevation changes ever attributed to human activity. The mechanism is aquifer-system compaction: when pumping removes groundwater faster than it recharges, fine-grained clay layers compress. Much of that compaction is permanent.
The story returned during California's recent droughts. During 2012–2016, USGS and NASA measurements documented renewed subsidence at rates that locally approached 30 centimeters per year. The subsidence damaged canals, aqueducts, bridges, and well casings — infrastructure that was built level and no longer is. The Sustainable Groundwater Management Act (SGMA) now requires groundwater sustainability agencies across the valley to monitor subsidence and manage pumping to avoid it.
Subsidence here is regional in cause but sharply uneven in effect. The bowls follow pumping patterns and geology, and the gradient — differential settlement — is what damages linear infrastructure. For a canal reach, a solar site on marginal farmland, or a facility near a documented bowl, the screening question is site-specific: what did this ground do, at what rate, and does it accelerate?
What the satellite archive holds here
The public Sentinel-1 radar archive, sampled at a representative point in this region. These numbers describe measurement availability — how often the satellites pass, and over what period — not ground movement. We compute movement per site, after the feasibility check.
- Radar acquisitions
- 328
- Revisit
- ~12 days
- Observed span
- 2022-01 → 2026-07
- Satellite tracks
- 4
Coverage stats as of 2026-07-14 · full Sentinel-1 archive extends back to 2015
What satellite radar can — and cannot — tell you
It can
- — Reconstruct a millimeter-scale movement history for stable radar reflectors (rooftops, pavement, rock, bare ground) on a specific site, from archive data
- — Show if the movement slows, stays steady, or accelerates — the trend shape that matters for decisions
- — Give you a dated record of what the ground did before a purchase, a design, or a dispute
It cannot
- — Measure surfaces that change between passes: dense vegetation, active construction, water
- — Replace geotechnical instrumentation, borings, or engineering judgment — it shows you where to look, not how to design
- — Tell you why the ground moves — it documents that it moves and how fast, as an input to the engineer who determines why
The honest economics: a commissioned InSAR study typically costs $10,000–30,000 and takes weeks. A self-serve report on one site costs $749, one time. The feasibility check before it is free — if the satellites cannot measure the site reliably, you pay nothing, and we say so.
Common questions
How much has the San Joaquin Valley sunk?
Historically, up to about 9 meters near Mendota by the 1970s, per USGS documentation. During the 2012–2016 drought, USGS and NASA measured renewed subsidence at rates that locally approached 30 cm per year. Rates vary strongly across the valley.
Does SGMA require subsidence monitoring?
Yes. Under California's Sustainable Groundwater Management Act, groundwater sustainability agencies must address six undesirable results in their plans. One of the six is land subsidence. This made subsidence data at site and basin scale a statutory concern for agencies and the consultants who support them.
Can satellite radar measure subsidence on farmland?
It depends on the site. Radar interferometry needs stable reflectors. Active fields scramble the signal, while structures, roads, canals, and bare ground measure well. The free feasibility check answers this before you spend any money — if a site fails, we say so.
Check a site in the California region
Draw your site, and you get a free feasibility report from the Sentinel-1 radar archive in about one minute. It tells you how many passes cover the site, how often, over what period — and if the satellites can measure it at all. If they cannot, the report says so.
Check your site freeTelluric readings come from satellite radar and are screening-grade: use them to decide where to inspect. They do not replace geotechnical instrumentation or engineering judgment. Read the methodology.