Sierra Nevada

The Sierra Nevada is a mountain range in the U.S. states of California and Nevada, between the California Central Valley and the Basin and Range Province. The Sierra runs 400 miles north-to-south, and is approximately 70 miles across east-to-west. Notable Sierra features include Lake Tahoe, the largest alpine lake in North America; Mount Whitney at 14,505 feet the highest point in the contiguous United States; and Yosemite Valley sculpted by glaciers out of 100-million-year-old granite. The Sierra is home to three parks, twenty wilderness areas, and two national monuments. These areas include Yosemite, Sequoia and Kings Canyon National Parks. The character of the range shapes its geology and ecology. More than 100 million years ago, granite formed deep underground. The range started to uplift 4 million years ago, and erosion by glaciers exposed the granite and formed the light-colored mountains and cliffs that make up the range. The uplift caused a wide range of elevations and climates in the Sierra, which reflected by the presence of five life zones. The climate of the Sierra Nevada is the climate of California. During the fall, winter and spring, precipitation in the Sierra ranges from 20 to 80 inches where it occurs mostly as snow above 6,000 feet. Summers are dry with low humidity; however, afternoon thunderstorms particularly during the North American Monsoon. Summer high temperatures average 42 to 90 degrees Fahrenheit. The growing season lasts 20 to 230 days, strongly dependent on elevation. The Sierra Nevada snowpack is the major source of water and a significant source of electric power generation in California. Many reservoirs were constructed in the canyons of the Sierra throughout the 20th century, Several major aqueducts serving both agriculture and urban areas distribute Sierra water throughout the state. However, the Sierra casts a rain shadow, which greatly affects the climate and ecology of the central Great Basin. This rain shadow is largely responsible for Nevada being the driest state in the United States. The height of the range and the steepness of the Sierra Escarpment, particularly at the southern end of the range produce wind phenomenon known as the "Sierra Rotor". This is a horizontal rotation of the atmosphere just east of the crest of the Sierras, set in motion as an effect of strong westerly winds.