Howell Mountain
Sub-AVA · Napa County · District 4
27 CFR 9.94 · established 1983-12-30 · last amended 1987-02-27
Heat class III · 1991-2020 normals
Climate normals in three numbers
, Apr 1 – Oct 31
11 GridMET cells cover this region
season rain, Apr 1 – Oct 31
55 mm of it in the , Sep 1 – Oct 31
Warm and cool vintages since 1980
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Rain across the season, and at harvest
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The boundary
Hovering a shaded region names it; a click opens its page.
Measured vineyard area
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Drought categories, year by year
Napa County — not Howell Mountain
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What's in the ground
5.9
pH, 1:1 water
12.7cm
, whole profile
80cm
to
Well drained
, dominant condition
Distribution across 29 · mean ◆, median │, p10–p90 bar
Dominant
- 32.0%
- 27.5%
- 19.8%
- 12.9%
- 2.7%
29 map units · soil described over 99.0% of the region’s area · 20.3% is water, rock outcrop or other non-soil · 97% of the described area has a restrictive layer within the profile.
Sand, silt and clay, against every other appellation
Loam
38% sand · 44% silt · 18% clay
Sandier than 31% of California appellations and clayier than 21%. Each grey point is one appellation’s topsoil; appellations nest, so this is a distribution of places rather than of land.
Plus 13% rock fragments by volume, which the triangle does not describe — the three fractions are of the fine-earth material only.
Elevation, slope and aspect
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Producers
A curated roster, not a census — only source-verified entries appear, 2772 published across the atlas.
Bearing acreage by variety
Napa County · District 4
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Price per ton
Napa County · District 4
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The appellation in federal law
The boundary, in the government’s own words (136 words)
(c) Boundaries. The Howell Mountain viticultural area is located in Napa County, California, and is part of the Napa Valley viticultural area. The exact boundaries of the viticultural area, based on landmarks and points of reference found in the approved maps, as follows: (1) Beginning at the 1,400 foot contour line at the intersection of Sections 15 and 16 in R6W/T9N of the Detert Reservoir Quadrangle U.S.G.S. map. (2) Then continuing in an east and southeast direction along the 1,400 foot contour line to the southeast corner of Section 23 in R5W/T8N. (3) Then in a generally northwest direction along the 1,400 foot contour line until it intersects the line between Sections 21 and 22 in R6W/T9N. (4) Then north along the Section 21/22 boundary line to the starting point at the 1,400 foot contour line.