Napa Valley received its designation as an AVA in 1981. Situated on 43,000 acres, Napa Valley is home to sub-appellations Los Carneros, Howell Mountain, Wild Horse Valley, Stags Leap District, Mt. Veeder, Atlas Peak, Spring Mountain District, Oakville, Rutherford, St. Helena, Chiles Valley, Yountville, Diamond Mountain District, Coombsville, Oak Knoll District of Napa Valley, and Calistoga. The Napa Valley floor is flanked by the Mayacamas Mountain Range on the western and northern sides the Vaca Mountains on the eastern side. The floor of the main valley gradually rises from sea level at the southern end to 362 feet above sea level at the northern end in Calistoga at the foot of Mount Saint Helena. The Oakville and Rutherford AVAs lie within a geographical area known as the Rutherford Bench in the center of the valley floor. The soil at the southern end of the valley consists mainly of sediments deposited by earlier advances and retreats of San Pablo Bay while the soil at the northern end of the valley contains a large volume of volcanic lava and ash. Several microclimates exist within the area due to various weather and geographical influences in the different sub-appellations. The open southern end of the valley floor is cooler during the growing season due to the proximity of San Pablo Bay while the sheltered, closed northern end is often much warmer. The eastern side of the valley tends to be arid because winter storms tend to drop much more precipitation on the western mountains and hills. Napa Valley is known for its world-class production of Cabernet Sauvignon but also produces Merlot, Cabernet Franc, Pinot Noir, Zinfandel, Chardonnay, and Sauvignon Blanc.