The Paso Robles AVA
With approximately 26,000 vineyard acres and more than 200 wineries, Paso Robles AVA is the largest geographic appellation in California. Its climate is influenced by proximity to the Pacific Ocean and Templeton Gap. A cool evening marine airflow moves east through the Gap keeping days sunny and warm and evenings cooler. Such conditions bring a longer growing season allowing vine fruits to mature and reach optimal ripeness. Heaviest rainfall occurs between January and March. Wine grape varieties grown in the area include Cabernet Sauvignon, Syrah, Merlot, Roussanne, Viognier, and Zinfandel.

AVA Districts
The Estrella District lies in the far north of the Paso Robles AVA and is on the East side. The topography comprises the rolling plains of the Estrella River valley and terraces. Elevations range 745 – 1819 feet.

Soils are typified by Quaternary alluvial soils of diverse ages across younger to older terraces with deep to moderate depth. Remnant patches of older valley fill at highest elevations of the District can be found.

The Paso Robles Willow Creek District sits to the West of Paso Robles and Templeton. The topography is high elevation mountainous bedrock slopes across a more erodible member of the Monterey Formation. Elevations run 960 – 1,900 feet topping out somewhat lower than the Highlands.

Soils are comprised of mostly bedrock from the middle and lower members of the Monterey Formation. Patches of alluvial soil along streams exist yet the District is largely calcareous with loams to clay loams.

The Geneseo District sits between the Estrella District to the north and the El Pomar District to the south. The topography is characterized by upfaulted hills through old river terraces along the Huerhuero–La Panza fault. Elevations run 740 – 1,300 feet.

Soils are considered old alluvial terrace and residual hillside soils of moderate depth with cementation of the gravelly Paso Robles Formation and older granites.

The Highlands District is to the far east of the greater Paso Robles AVA. The topography is typified as old Pliocene–Pleistocene erosional surface across the Simmler, Monterey and Paso Robles formations below the La Panza Range. The elevations range 1,160 – 2,086 feet and represent some of the highest points in the greater AVA.

Soils are comprised of deep, sometimes cemented alluvial soils; old leached alkaline soils common, with younger sandy soils along active streams.

Paso Robles (full name: El Paso de Robles ‘The Pass of the Oaks’) is a city in San Luis Obispo County, California, United States. Located on the Salinas River north of San Luis Obispo, California, the city is known for its hot springs, its abundance of wineries, production of olive oil, almond orchards, and for playing host to the California Mid-State Fair, as well as being the number one skateboarding community nationwide.

Geography
Paso Robles is located at 35°37′36″N 120°41′24″W, approximately halfway between the cities of Los Angeles and San Francisco. Paso Robles is where the region of Southern California ends. The elevation of Paso Robles ranges from 675 to 1,100 feet (340 m), but the majority of the main downtown area of the city sits at about 740 feet (230 m) above sea level. According to the United States Census Bureau, the Paso Robles city limits contain a total land area of 19.4 sq mi (50.3 km2), 98.43% of it land and 1.57% of it water.

The topography of the area consists of gentle rolling hills on the eastern half of the city, and foothill peaks which rise in elevation to the Santa Lucia Coastal Range on the west, which are all blanketed in the Californian chaparral environment, which is mainly dry grassland and oak woodland. Simply “Paso,” as it is referred to by locals, sits on the eastern foothills of the Santa Lucia Coastal Mountain Range, which lies directly to the West of the city, and runs in a North-South direction, starting at Monterey, then runs down South to its terminus, in the San Luis Obispo area. The city is located at the southern end of the fertile Salinas River Valley, which is centered in between the Temblor Range (including the San Andreas Fault), which lie about 28 miles (45 km) to the East, and the Santa Lucia Coastal Range, which lie directly west, rising up from the city’s western border. Paso Robles sits at the border where northern San Luis Obispo County and southern Monterey County meet, and is situated roughly 24 miles (39 km), or 20 minutes, inland from the Pacific Ocean.

Climate
The Paso Robles area actually consists of two different climate types and classifications, as based on the Köppen climate classification (KCC) system, which are KCC type BSk, a semi-arid, dry, steppe-type climate, and KCC type Csb, which is the typical, coastal Californian & ‘Mediterranean’ type. The area receives a mixture of these two types of climates, but the primary climate is defined by long, hot, dry summers and brief, cool, sometimes rainy winters. Paso Robles enjoys long-lasting, mild autumns and occasional early springs, giving the region a unique climate suitable for growing a variety of crops (ranging from primarily grapes, to olives, to almonds and other tree nuts). The city receives an average annual rainfall of about 14.71 inches (374 mm) per year, and most of this precipitation falls during winter and early spring. Paso Robles often receives less than 10 inches (250 mm) of rain per year and typically, no rain falls from May through September. Summers in Paso Robles tend to be very hot, with daily temperatures frequently exceeding 100 °F (38 °C) from late June to as late as mid September, and occasionally exceeding 110 °F (43 °C). Paso Robles’ summers feature an unusually large daytime-nighttime temperature swing, where there may be a profound temperature difference, as much as 50 °F (28 °C), between the daytime highs and the overnight lows. Winters are often very cool and moist, with daytime temperatures reaching into the low 50s°F (10 °C). Mornings and nights differ from the daytime average, as they tend to very frigid (especially in December and January), where lows reach as low as 25 °F (−4 °C). Due to the somewhat close proximity to the Pacific Ocean, the marine layer occasionally makes it over the coast range and into Paso Robles, creating occasional fog. However, unlike typical California coastal marine fog in areas such as San Francisco, this fog is never long lasting, and typically burns off before 10am.

Source:Wikipedia, Appelation America