A buyer finds forty acres of irrigated pasture outside Escalon, priced right for the size and the crop. The tour goes well. The offer gets accepted. Then the preliminary title report comes back, and on page three sits a line most people skip past on a first read: the parcel is enrolled in a Williamson Act contract.
That single line changes the transaction. The contract runs with the land, not with the seller, so the buyer inherits it along with the reduced property tax it carries. Getting out of it isn't a phone call. It's either a 10-year phase-out with rising taxes each year, or a cancellation that requires the county to make specific findings and carries its own financial penalty. Either path has to be initiated with written notice, and if the owner wants to start that clock, county rules require at least 90 days notice before the contract's annual renewal date.
None of that shows up in the listing photos. It shows up in escrow, usually right around the time a buyer thought they were close to done.
What a Williamson Act contract actually restricts
San Joaquin County uses the Williamson Act, formally the California Land Conservation Act of 1965, to keep land in agricultural production by trading a lower property tax assessment for a landowner's commitment to farm use. To even qualify, a parcel has to sit inside a county-designated Agricultural Preserve, which requires a minimum of 100 contiguous acres, and the standalone contract itself requires at least 80 acres of agricultural land.
The tax benefit is real and it's the whole reason these contracts exist. It's also why a buyer can't simply assume they'll cancel it after closing if their plans change. The county's own guidance describes two ways out:
- Non-renewal. Either party files notice and the contract terminates over a 10-year term, with the tax assessment climbing back toward market value each year until it fully resets.
- Cancellation. A faster exit, but it requires specific findings by the county and comes with its own financial penalty for ending the contract early.
The rules around these contracts are still moving. A 2026 bill working through the state legislature, AB 1156, would change how Williamson Act land converts into a solar-use easement, adjusting who can waive cancellation payments and under what conditions. That's not a footnote. It's a sign that a buyer's exit options on ag-preserve land can shift year to year depending on what Sacramento does next, which is one more reason to check contract status before writing an offer instead of after.
The bigger question the contract doesn't answer
Suppose the parcel isn't under a Williamson Act contract at all. The land is clean, the price looks fair, the acreage checks out. There's still a second question that matters more than almost anything on the listing sheet, and it's one most buyers never think to ask: which groundwater subbasin is this parcel sitting in.
San Joaquin County isn't one water story. It's at least two, and they've diverged sharply.
The Tracy Subbasin, which covers roughly the southwestern third of the county including Tracy, Lathrop, and the growing community of Mountain House, got its Groundwater Sustainability Plan approved by the California Department of Water Resources with language most farmland doesn't get to claim. The subbasin has experienced no chronic lowering of groundwater levels, no significant reduction in storage, no surface water depletion, and no land subsidence from pumping. The county's public works director called the required work to keep it that way "relatively modest."
The Eastern San Joaquin Subbasin, which covers the larger, more agriculturally intensive stretch of the county, tells a different story. It's designated by the state as being in critical overdraft, meaning more water comes out of the ground each year than goes back in. During the 2022 drought year alone, the subbasin lost about 122,000 acre-feet of groundwater storage. Chronic overdraft like that carries real consequences: land subsidence, degraded water quality, and infrastructure risk from shifting ground.
| Subbasin | State designation | Recent trend | What it means for a buyer |
|---|---|---|---|
| Tracy Subbasin (Tracy, Lathrop, Mountain House area) | Approved GSP, no chronic overdraft flagged | No significant storage decline, no subsidence reported | Groundwater access has held up; fewer surprises on well reliability |
| Eastern San Joaquin Subbasin (broader county farmland) | Designated in critical overdraft | Lost roughly 122,000 acre-feet of storage in 2022 alone | Pumping limits and allocation rules are more likely to tighten before 2040 |
That's not a difference of degree. It's the difference between buying into a subbasin the state considers on track and one it has flagged as needing major correction before the 2040 sustainability deadline set by California's Sustainable Groundwater Management Act. A well that pumps reliably today in an overdrafted subbasin isn't guaranteed to pump the same way in ten years if the local groundwater sustainability agency tightens allocations, which several subbasins across the broader San Joaquin Valley have already started doing.
What the water question is actually worth
This is where the subbasin distinction stops being an abstraction and starts showing up in price.
The USDA's most recent land values summary put California's statewide average farm real estate value at $13,700 per acre for 2025, land and buildings combined. That's the kind of number that tells you almost nothing about a specific parcel, because it flattens everything from unirrigated foothill grazing land to a fully wired almond orchard into one figure.
The real spread shows up once you get local. Industry appraisers tracking 2026 California land values have put productive orchard ground with reliable access to both surface water and groundwater in the range of roughly $25,000 to $42,000 per acre in the better-watered districts around Lodi and the surrounding county. Less-secure ground, meaning parcels more exposed to pumping restrictions or thinner surface water rights, has seen noticeably steeper discounts in the same market. Agricultural land values across the county have also faced general downward pressure through 2026 from a mix of softer commodity prices, higher interest rates, and the ongoing rollout of SGMA restrictions, with permanent-crop properties in water-challenged areas showing the most softening.
Put plainly: two forty-acre parcels a few miles apart, same crop, same soil type on paper, can land tens of thousands of dollars apart per acre once a buyer's lender or appraiser factors in which subbasin the water comes from. That gap is the actual thesis of this entire due-diligence exercise. The listing price is a starting point. The subbasin is the multiplier.
What water security looks like in an actual listing
A recent listing for the Rockin CB Ranch, a 163-acre property in Escalon, is a useful example of what a well-documented water position looks like on paper. The marketing described the ranch as comprised primarily of irrigated pasture and row crops with good water supply, the kind of specific, verifiable claim that holds up under scrutiny. Other Escalon-area listings have gone further, naming the South San Joaquin Irrigation District as the surface water source alongside a private agricultural well, giving a buyer two distinct, checkable water sources rather than one vague assurance.
That level of detail is worth more than acreage or a nice barn photo. A listing that names the irrigation district and the well status is telling a buyer something a generic description never will: that the seller has already done the homework a lender or appraiser is going to demand anyway.
Before you write an offer
A few checks take less time than a single showing and can save weeks in escrow later:
- Ask the listing agent or title company whether the parcel carries an active Williamson Act or Farmland Security Zone contract, and if so, request the contract terms and remaining years directly from the county assessor.
- Confirm which groundwater subbasin the parcel sits in and whether that subbasin's groundwater sustainability agency has adopted pumping allocations or is discussing them.
- If the property relies on a private well, check with San Joaquin County's Environmental Health Department on permit history. Well construction permits are only valid for one year from issue, with one possible one-year extension, so an old or expired permit on file is worth a direct question to the seller.
- Ask specifically whether irrigation comes from a district, a private well, or both, and get that in writing rather than as a verbal assurance.
None of these steps require a land-use attorney to start. They require asking the right question before the offer goes in, not after the title report lands.
The takeaway
A rural parcel in San Joaquin County is never just an acreage number and a price. It's a contract status and a water future, and both of those can move the real value of the land far more than the difference between a nice barn and an average one. The buyers who do well here aren't the ones who fall for the prettiest listing photo. They're the ones who ask about the subbasin before they ask about the barn.
If you're weighing a rural or agricultural property in San Joaquin County, or trying to figure out what a parcel is actually worth once water and contract status are factored in, Lori Cabral combines a formal agriculture background with full-service brokerage experience across the county's suburban and rural markets. Get your free Home Market Analysis and find out what your land is really worth before you list or make an offer.
