There are over 107 American Viticultural Areas (AVAs) including Napa, Russian River Valley, Ruhterford and Sonoma Valley. The Central Valley is the largest wine region covering about 300 miles from the Sacramento Valley south to the San Joaquin Valley. This specific region mentioned produces about 75% of all California wine grapes. In Central Valley you will find Sierra Foothills AVA, a highly respected area would be Lodi AVA.
You can find a list of popular Central Valley Wineries right here.