Section 9.166 - Diamond Mountain District(a)Name. The name of the viticultural area described in this section is "Diamond Mountain District."(b)Approved map. The appropriate maps for determining the boundary of the Diamond Mountain District viticultural area are two 1:24,000 Scale U.S.G.S. topography maps. They are titled:(1) Mark West Springs, CA 1993(c)Boundaries. The viticultural area is located in Napa County, California. The beginning point is where the boundary between Napa and Sonoma counties intersects Petrified Forest Road in Section 3 of Township 8 North, Range 7 West, Mount Diablo Base and Meridian on the Mark West Springs map; (1) Then north and east along Petrified Forest Road approximately 1.9 miles to the point where it intersects the 400-foot contour just east of Section 35 of Township 9 North, Range 7 West, Mount Diablo Base and Meridian, in the Mallacomes land grant;(2) Then generally east southeast along the 400-foot contour approximately 6.5 miles to the point where it intersects Ritchey Creek in Section 3 of Township 8 North, Range 6 West, Mount Diablo Base and Meridian;(3) Then west southwest along Ritchey Creek approximately 2.2 miles to the point where it intersects the boundary between Sections 17 and 20 of Township 8 North, Range 6 West, Mount Diablo Base and Meridian;(4) Then due west in a straight line along the section boundary approximately 0.8 miles to the point where it intersects the boundary between Napa and Sonoma Counties between Sections 18 and 19 of Township 8 North, Range 6 West, Mount Diablo Base and Meridian;(5) Then generally northwest along the boundary between Napa and Sonoma Counties approximately 4.2 miles to the point where it intersects Petrified Forest Road, to the point of beginning.T.D. ATF-456, 66 FR 29698 , 6/1/2001