Paso Robles is the third American Viticultural Area (AVA) located in northern San Luis Obispo (SLO) County, California. The wine appellation was established on October 4, 1983 as the nation's 44th, the state's 29th and the county's fourth AVA by the Bureau of Alcohol, Tobacco and Firearms (ATF), Treasury after reviewing the petition submitted by Martin Brothers Winery accompanied by 51 signatures of local grape-growers and wineries proposing a viticultural area named "Paso Robles." The AVA encompasses 609,673 acres (953 sq mi) with approximately 18,500 acres (7,487 ha) cultivated with wine grapes known for their heritage varietal Zinfandel, Cabernet Sauvignon, and Rhône-style wines.