Paso Robles received its designation as an AVA in 1983. Sitting on 666,618 acres in San Luis Obispo County, Paso Robles is home to eleven sub-districts, including: Adelaida District, Creston District, El Pomar District, Paso Robles Estrella District, Paso Robles Geneseo District, Paso Robles Highlands District, Paso Robles Willow Creek District, San Juan Creek, San Miguel District, Santa Margarita Ranch, and Templeton Gap District. By far the largest region in San Luis Obispo County, Paso Robles has over 19,000 acres under vine. The region features a mixture of silica clay and chalky lime soils. Closer to the Pacific, the western edge of Paso Robles has warm daytime temperatures, often topping 90 degrees during the peak of the growing season. The grapes are cooled by the maritime breezes coming in off the Pacific Ocean. Moving east across the region, the climate becomes more aired and drier than its western counterpart. In the east, fruit ripens more quickly than in the west, giving it bright flavors with low acidity and tannin structure. The more famous western region features a longer growing season allowing the fruit to take its time to ripen and develop a balance of acidity and tannin. Cabernet Sauvignon is the varietal that is most prevalent in the eastern regions of Paso Robles while Rhone varietals such as Viognier and Syrah dominate the west. In all, there are over 40 grape varietals grown in Paso Robles, and the region has become well known for its blends.