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

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

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

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

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

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.

In the 1990's, some growers began to support the idea of dividing the valley floor of Napa up into several sub-AVA's, which would be named after the towns of the area, much like Bourdeaux's appellations. The effort to create these AVA's was never fully completed because the phylloxera outbreak became too demading on wine makers, but some of them were created, and are valuable to understand. Here they are:

Calistoga

While Calistoga is not an official AVA, it does produce a certain style of wines. The area is 10-20 degrees warmer than the town of Napa during the day, but at night the Russian River helps balance the acidity by cooling it off at night, extending the growing season. The soil here is mostly gravel, which provides excellent drainage, stressing the vines enough to reduce yields and produce powerful and concentrated wines. Cabernet Sauvignon is the most common varietal in Calistoga.

St. Helena

St. Helena is an official AVA, and was designated one in 1995. It is very close to Calistoga, but is just a little bit cooler. This is very much a red grape area, with Zinfandel and Petite Syrah doing very well. The classic description for these wines is "elegant."

Rutherford

Rutheford became an AVA in 1993, and was originally going to be divided further with part designated as the Rutherford Bench. The bench is an alluvial fan that runs along the side of the valley and is responsible for some of the most sought-after wines of Napa Valley. The bench actually extends far beyond Rutherford into Oakville and Yountville. The total area of Rutheford is about 6,700 acres, of which only about 2,800 is in the bench.

Oakville

The Oakville AVA is a littel south from Rutherford, and does include sections of the rutherford bench mentioned above. Some wine makers have expressed a desire to rename this portion the Oakville Bench, but have so far been unsuccessful. Like the other areas to the North, Oakville is primarily Cabernet Sauvigon territory, but thanks to morning fog and the cooling influence of the San Pablo Bay, Oaville also produces Chardonnay, Sauvignon Blanc, and a little Sangiovese.

Yountville

Yountville became an AVA in 1999. It's composed of about 8,200 acres of land, but less than half of it is dedicated to vines. The cooling influence of the San Pablo Bay is quite strong in Yountville, which makes it only marginally successful at producing Cabernet Sauvignon. Chardonnay is considered to be much more successful in this area.

Stag's Leap

Stag's Leap became an AVA in 1989, and got its name because of a basalt outcropping of the Atlas Mountains that hangs out over the vineyards, resembling a Stag. The basalt moderates the night time cooling effect often seen in the southern area of Napa by reflecting heat back down onto the valley floor. This makes it the perfect place to grow Cabernet Sauvignon.

Oak Knoll District

Oak Knoll was designated as an AVA in 2002, and is one of the most southern and therefore coolest AVA's in Napa. The most promising grape here is Merlot, which has been gaining a reputation, but it also produces Cabernet Sauvignon, Pinot Noir, and Chardonnay.

Wild Horse Valley

Wild Horse Valley became an AVA in 1988. It does not have any wineries, but many wine makers use the grapes grown here to make wine. It's located about 1,000 feet above sea level, a little bit east of Carneros. It is very cool and breezy here. The primary grapes planted include Pinot Noir, Chardonnay, Riesling, and Viognier.

The Napa Valley is the name of a county, but it is also a general AVA that contains many smaller AVA's within itself. The area is only 30 square miles, and it has about 250 wineries. The Napa Valley soil consists of a complex range of different sedimentary soils, caused by repeated flooding of an uplifted seabead over thousands of years. As a result the area has about 150 different soil types! Generally temperatures in Napa increase as one travels north, but higher elevations in towns like Calistoga and the cooling effect of the Russian River can lessen the heat. Napa has 40,000 acres under vine, and produces about 5% of California's total wine production.