(a) Name. The name of the viticultural area described in this section is “Howell Mountain.”

(b) Approved maps. The appropriate maps for determining the boundaries of the Howell Mountain viticultural area are four U.S.G.S. topographic maps in the 7.5 minute series, as follows:

(1) “Detert Reservoir, CA.,” 1959 (photorevised 1980).

(2) “Aetna Springs, CA.,” 1958 (photorevised 1981).

(3) “Calistoga, CA.,” 1958 (photorevised 1980).

(4) “St. Helena, CA.,” 1960 (photorevised 1980).

(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.