Central Valley
The Central Valley is the vast agricultural heartland of California, tucked between the coastal mountain ranges and the Sierra Nevadas to the east. While the state's glamor wines largely come from coastal appellations, the volume often comes from the Central Valley.
In general terms, this region is much warmer than coastal areas that benefit from the cooling influence of the Pacific. This allows for the production of large volumes of wine that is generally higher in alcohol and lower in acidity. As such it is the engine of the jug-wine industry, but cooler areas provide the bulk of fighting-varietal production. In short, while the coast gets all the press, the Central Valley pays much of the bills in the Golden State.