California’s climate is quite varied, which is not surprising given the large area of the state. In rough terms the climate on the coast is similar to the Mediterranean with warm summers and mild winters. Summer in the Central Valley is exceptionally hot and dry, while summer in the area immediately behind the coast is much moister and can be misty.
The highest temperatures are in the Central Valley and the mildest are on the coast. The North Coast vineyards get the most rainfall. The soil is also varied as a result of the many earthquakes that hane occured throughout the area. The soil varies from alluvial and sedimentary deposits to strata of volcanic origin.
The notion of terroir that is so strong in Europe is not given much credence in California. The variety of grape is far more likely to be chosen as suitable for the climate than the soil.