The mountain ranges on either side of Napa Valley are somewhat different from the valley floor. The growing season is longer, with cooler days and warmer nights. There is often quite a bit of volcanic soil, which makes growing and irrigation harder, reducing yields and producing smaller berries. Due to these factors, the mountain wines tend to be more tannic and more intensely flavored. The western border of Napa is the Mayacamas mountain range, which comprises Diamond Mountain, Spring Mountain, and Mount Veeder. On the eastern side of the valley lies Howell Mountain and Atlas Peak. The eastern mountains tend to be more wooded and get a lot more rain than the dry western sides, which tend to produce softer and lighter wines. All of them are usually age-worthy though.
Diamond mountain is the most Northerly AVA in the Mayacamas. It was established in 2001, comprises 5,000 acres, of which only 500 acres are under vine. The most common grapes are Cabernet Sauvignon, Merlot, and Zinfandel.
Spring Mountain was established as an AVA in 1993. It has many different microclimates, and covers 8,600 acres. The best grapes here are Cabernet Sauvignon, Petite Syrah, Pinot Noir, and Zinfandel.
Mount Veeder became an AVA in 1990. All the vineyards are planted at elevations between 600-2,700 feet, and it falls in the Regions 1 and 2 classification in the heat summation index. The most common grapes here are Cabernet Sauvignon and Chardonnay, with smaller pockets of Zinfandel, Sauvignon Blanc, Merlot, Syrah, and Viognier.
Howell Mountain is Napa's oldest AVA, established in 1984. Due to less rain, cooler temperatures, and volcanic and rocky soil, the area has lower yielding crops. The vineyards are all at altidudes ranging from 1,600-2,000 feet. Cabernet Sauvignon, Zinfandel and some Merlot are the most common grapes here, small amounts of Chardonnay as well.
Atlas peak is just south of Howell Mountain on the east side of Napa Valley. It covers about 11,000 acres, but has only a few wineries. The main winery, which is called Atlas peak, has committed to growing Sangiovese.