Despite its limited acreage, Napa Valley is a diverse growing region with many microclimates and varied soil types. Over the 30 miles from the cool San Francisco Bay north through Oakville, Rutherford, St. Helena and Calistoga, the average temperature can increase 10 percent. So cool-weather varieties like Chardonnay and Pinot Noir thrive in Carneros, at the southern end of the region; warm-weather grapes like Cabernet Sauvignon, Merlot and Sauvignon Blanc fare better in the north.