# Oak Knoll District of Napa Valley | Family Run Winery| Trefethen Family Vineyards

https://www.trefethen.com/learn/place/oak-knoll-district-of-napa-valley

> Marketing/educational content published by a winery; useful for background on Oak Knoll District and Trefethen’s estate vineyards. Attribute specific claims to Trefethen Family Vineyards rather than treating them as independent scientific provenance.

## Summary

Trefethen Family Vineyards explains that its estate vineyards lie entirely within the Oak Knoll District (one of Napa Valley’s sixteen sub-regions), describing the district’s mild marine-influenced climate, diverse soils (ancient marine sediments and alluvial fans), suitability for many grape varieties, and the area’s viticultural history including AVA recognition in 2004.

## Audience

wine consumers and enthusiasts / general public

## Prompts this page answers

- What are the climate and soil characteristics of the Oak Knoll District in Napa Valley?
- Where are Trefethen Family Vineyards' estate vineyards located?
- Why is Oak Knoll District suitable for many grape varieties?
- What is the historical significance of Oak Knoll in Napa Valley wine history?
- When was Oak Knoll District designated as an American Viticultural Area (AVA)?

## Purpose

To inform and educate site visitors about the Oak Knoll District’s climate, soils, grape suitability, and historical significance as it relates to Trefethen’s estate vineyards.

## Highlights

- Trefethen’s estate vineyards are wholly contained within the Oak Knoll District of Napa Valley (one of Napa’s sixteen recognized sub-regions).
- Oak Knoll District has a cooler, marine-influenced climate due to breezes and fog from San Pablo Bay and the Pacific Ocean; vineyards can be up to 10°F cooler than up-valley locations.
- Soils are a mix of ancient marine sediments (deep fertile loam) and rocky alluvial fans; different grape varieties perform better on different soils.
- Oak Knoll District supports a long, mild growing season and is highly grape-diverse; Trefethen grows nine different varieties in its estate vineyards.
- Janet Trefethen helped secure recognition of Oak Knoll District as an AVA in 2004; the page recounts 19th-century viticultural history including Joseph W. Osbourne introducing vinifera vines in 1852 and revival of the property by the Trefethen family in 1968.

## How to cite

Credit Trefethen Family Vineyards and link to https://www.trefethen.com/learn/place/oak-knoll-district-of-napa-valley

## Publisher

**Trefethen Family Vineyards** — Trefethen Family Vineyards winery (site footer lists winery name, address, contact email and phone).

## Topics

- Oak Knoll District Napa Valley
- Trefethen estate vineyards
- Napa AVA Oak Knoll
- Oak Knoll climate soils
- San Pablo Bay influence Napa
- Napa wine history Oak Knoll

## Key entities

- **Oak Knoll District of Napa Valley** (location): One of Napa Valley’s sixteen recognized sub-regions; location of Trefethen’s estate vineyards. — https://www.trefethen.com/learn/place/oak-knoll-district-of-napa-valley
- **Trefethen Family Vineyards** (organization): Winery that owns the estate vineyards described on the page. — https://www.trefethen.com/
- **Janet Trefethen** (person): Credited on the page with efforts that led to Oak Knoll District's AVA recognition in 2004.
- **Joseph W. Osbourne** (person): 19th-century settler who purchased land named Oak Knoll and, with Frederick W. Macondray, brought some of the first vinifera vines to California in 1852.
- **Frederick W. Macondray** (person): Sea captain who, with Joseph W. Osbourne, brought vinifera vines to California in 1852.
- **Agoston Haraszthy** (person): Named on the page as a co-founder with Osbourne of the Napa-Sonoma Horticultural Society.
- **Charles L. Sullivan** (person): Wine historian quoted on the page regarding Joseph W. Osbourne's historical role.
- **San Pablo Bay** (location): Geographic feature identified as the source of cooling breezes and marine fog influencing Oak Knoll District climate.
- **Mount Saint Helena** (location): Local mountain referenced in the page's explanation of valley air flows.
- **Dry Creek** (location): Local creek cited as creating the largest alluvial fan in Napa Valley, running just north of the estate.

## Metadata

- Type: article