Knights Valley is an American Viticultural Area (AVA) located in Sonoma County, California. As one of the five original viticultural areas in the county, Knights Valley was established on October 21, 1983 by the Bureau of Alcohol, Tobacco and Firearms (ATF), Treasury after reviewing the petition submitted by The Knights Valley Wine-Growers Committee, an organization of grape/wine industry members, signed by 16 persons, to establish a viticultural area in northeastern Sonoma County named "Knights Valley." The area encompasses approximately 36,240 acres (57 sq mi) with over 30 growers cultivating 2,000 acres (809 ha) under vine. In the easternmost Sonoma County region, Knights Valley has the warmest climate in the county. The northernmost section of the boundary line runs slightly to the north of Pine Mountain; the southernmost section of the boundary line borders the petrified forest area immediately to the north of Porter Creek. The Sonoma County line bordering Lake County and Napa County forms the eastern section of the boundary of the viticultural area. The easternmost section of the boundary line abuts the boundaries for the Alexander Valley and Chalk Hill viticultural areas. The appellation is the border separating Sonoma County from the Napa Valley.