Oakville Vineyards: Ag Preserve Zoning, Measure P, Winery Rules and Water

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

Oakville is a mid-valley Napa appellation that runs across the valley floor between Yountville and Rutherford, from the 500-foot contour of the Mayacamas Range on the west to Rector Creek and the hills on the east. For an owner, the big questions are usually less about where to plant and more about what Napa County’s agricultural rules allow on a given parcel, from homes and wineries to visitor use, and how the parcel fits the county’s groundwater program.

Oakville at a glance

Where the appellation runs

The Oakville boundary at 27 CFR 9.134 begins on the Yountville quadrangle where the Silverado Trail meets Skellenger Lane. It follows Skellenger Lane southwest to the Napa River, runs down the riverbed about 0.4 mile, follows an unnamed stream to the railroad track, then uses bearings along specific Assessor’s parcel lines before heading west to the 500-foot contour of the Mayacamas Range. On the south it follows Hopper Creek and the 300-foot contour around the Yountville Hills. On the east it runs up Rector Creek past the Silverado Trail to the Rector Reservoir spillway, then back west to the Skellenger Lane starting point.

Because the northern line is shared with Rutherford and is drawn partly along recorded parcel lines, a ranch that straddles Skellenger Lane or the parcel boundaries near the Mondavi entry road can include blocks entitled to different names. The western and eastern edges are set by elevation, so upper hillside blocks above the 500-foot line on the Mayacamas side sit outside Oakville even when the property is one parcel. The whole area is inside the Napa Valley AVA, first established in 1981. See our Napa Valley appellation overview for how the nested districts fit together.

Agricultural Preserve zoning and Measures J and P

Oakville vineyard land is shaped by a 1968 decision. Napa County’s Agricultural Preservation and Land Use Element of the General Plan records that the Agricultural Preserve was established that year, and land designated Agricultural Resource, which typically covers the valley floor, carries a 40-acre minimum parcel size (Policy AG/LU-21). Hillside land designated Agriculture, Watershed and Open Space carries a 160-acre minimum (AG/LU-20). On the zoning map these correspond to the Agricultural Preserve (AP) and Agricultural Watershed (AW) districts; our Napa AP and AW zoning guide walks through what each allows.

Voters then locked those designations in. Under Measure J, approved in 1990, redesignating agricultural land to other uses requires a public vote. Voters adopted Measure P in 2008, and the General Plan states that policies derived from Measures J and P cannot be amended or removed without voter approval until after December 31, 2058, unless voters extend that date. For an Oakville buyer, this means the zoning you buy is the zoning you will likely have for decades: a parcel under 40 acres is not a path to a subdivision, and agricultural land is not going to be rezoned for other uses without an election.

Building a home on agricultural land is possible within those rules, but the size, siting and accessory structures are controlled. See building a home on Napa ag land.

Wineries: the Winery Definition Ordinance and use permits

Napa County treats a winery as agricultural processing, and the General Plan (AG/LU-13) carries forward the 1990 Winery Definition Ordinance. Two of its rules matter most to an Oakville buyer. Wine produced at a winery approved after the ordinance must use at least 75% Napa County grapes, and tours and tastings at those newer wineries are by appointment only. Retail sales, limited food service and marketing are allowed only as accessory uses to production. Our Winery Definition Ordinance guide covers the history.

The county’s winery use permit application shows what a new or expanded winery has to document: a Water Availability Analysis or groundwater study under the county’s well permit standards, septic and process wastewater feasibility, trip generation (with a full traffic study usually expected at 110 or more new daily trips), biological and cultural studies, and a hydrology analysis if the site is in a floodplain or floodway. Winery coverage is capped at 25% of the parcel or 15 acres, whichever is less, and accessory space at 40% of the production area. For a smaller estate, the county’s micro-winery use permit allows up to 5,000 gallons of capacity and 5,000 square feet of enclosed space, with at least 75% of grapes from the same or contiguous parcels, a cap of 20 average daily trips and no marketing events. It is available only in the AP and AW zones. See also our Napa winery use permit guide and Napa Valley wineries for sale.

An existing use permit generally stays with the property, so its exact terms (production gallons, visitors, events, hours) are among the most important documents in an Oakville winery sale. Get the permit, all modifications and the county’s compliance history before you write an offer.

Water: the Napa Valley Subbasin

Oakville’s valley floor overlies the Napa Valley Subbasin. The Napa County Groundwater Sustainability Agency is responsible for its Groundwater Sustainability Plan, which DWR approved on January 26, 2023. On December 9, 2025, the agency adopted Resolution 2025-05 setting groundwater sustainability fees for properties in the subbasin, with properties served inside the municipal districts of Calistoga, St. Helena, Napa and Yountville excepted. Unincorporated Oakville parcels are not in those districts, so expect the fee to apply and ask the seller for the parcel’s current bill. The agency also publishes the county’s well permit standards and Water Availability Analysis requirements, updated January 10, 2024. Our Napa groundwater rules guide and the blog post on how the subbasin fee is calculated go further.

The Napa River below Oakville

A short stretch of the Napa River forms part of Oakville’s northern boundary. According to Napa County’s restoration program, the Rutherford Reach project runs downstream as far as the Oakville Cross Road bridge, and the Oakville to Oak Knoll project picks up there, covering about nine river miles from Oakville Cross Road to Oak Knoll Avenue, funded through Measure A and state and federal grants, with management of invasive and Pierce’s disease host plants as part of the work. For riverside parcels, ask how the project touches the property and whether any agreement with the county or flood control district is recorded.

Replanting, erosion control and hillside edges

On an established vineyard, the usual permit question is replanting. Napa County’s erosion control plan process requires an approved plan for agricultural grading on slopes over 5%, including vineyard replants on those slopes, under the Conservation Regulations in Chapter 18.108. Replant plans on qualifying sites can follow a faster track if prepared by a county-listed consultant. Flat valley-floor blocks below 5% generally fall outside that requirement, but the benches and hillside edges near the Mayacamas and the Yountville Hills may not. See our vineyard development guide.

Some parcels also carry Williamson Act contracts. In Napa County these require AP or AW zoning, a bona fide agricultural use and at least 10 acres of prime land or 40 acres of non-prime land, on a rolling 10-year term; new applications are taken each September. See our Williamson Act guide.

A due diligence list for an Oakville vineyard

Pair this with our full vineyard due diligence guide:

• Map every block against 27 CFR 9.134, especially near Skellenger Lane, the Mondavi-area parcel lines and the 500-foot contour.
• Confirm the General Plan designation and zoning (AP or AW) and the legal lot status of each parcel.
• Confirm whether a home, second unit or farm housing can be added under current rules.
• For a winery, get the use permit, every modification, production and visitor limits and compliance history.
• Confirm the grape-sourcing plan meets the 75% Napa County rule if a winery is involved.
• Pull well logs, any Water Availability Analysis and the current subbasin groundwater fee.
• Check septic and process wastewater capacity; see winery wastewater.
• Identify blocks over 5% slope that would need an erosion control plan to replant.
• For riverside parcels, check FEMA flood zone and any river restoration agreements.
• Pull any Williamson Act contract.
• Review vine age, rootstock and virus status; see red blotch diagnosis.
• Get insurance quotes and check fire hazard zone mapping early.

Questions people ask

Sources & notes

1. eCFR: 27 CFR 9.134, Oakville
2. eCFR: 27 CFR 9.23, Napa Valley
3. Napa County: General Plan, Agricultural Preservation and Land Use Element
4. Napa County: Use Permit / Administrative Permit Application, Winery Uses
5. Napa County: Use Permit, Micro-Winery
6. Napa County: Groundwater Sustainability
7. Napa County: Habitat Restoration & Monitoring (Napa River projects)
8. Napa County: Erosion Control Plan Review & Approval Process
9. Napa County: Williamson Act & Agricultural Preserve Contracts

General information, not legal or tax advice. Last reviewed November 2026 by Matthew Martinez.

Related: Napa Valley vineyards · Oakville real estate guide · Yountville real estate guide · Rutherford vineyards · Stags Leap District vineyards · Vineyard due diligence · Vineyard water rights · All vineyard and winery guides