SIERRA NEVADA MOUNTAINS [Span. for "Snowy Peaks"], a geologically young mountain range in western United. States which begins at Tehachapi pass in southern California, ex tends northward 43o m. as part of the boundary between Cali fornia and Nevada, and ends in southern Oregon where it merges with the Klamath or Siskiyou mountain group. Their geologic history is a fascinating record of relatively recent earth move ment. Where they now rise the waters of Paleozoic and early Mesozoic seas laid down sediments, which were intruded by granitic magmas and compressed by heavy folding into lofty summits in mid-Mesozoic time. During the early Cretaceous these newborn mountains were peneplaned, to be uplifted and planed down repeatedly throughout Cretaceous and Tertiary time. Beginning probably in Cretaceous time profound faulting proceeded with down throw toward the east, and a gigantic block of the earth's surface, probably the largest single such block on the face of the earth, began tilting toward the Pacific, forever shutting out its waters from the great interior basin. By the close of Tertiary time a steaming expanse of volcanic mud had buried the whole of the northern Sierra, a chaotic contrast to the peaceful rolling hills of the Miocene time, clothed by ver dant tropical vegetation. As the great block tilted more and more, the streams cut deeper and more sharply into the tuff covered surface and during the late Tertiary and early Quaternary shaped the steep-walled canyons and rugged summits that char acterize the Sierra Nevadas, then clothed by a luxuriant vege tation temperate instead of tropic in type. With the beginning of the Pleistocene ice age the summits became mantled in deep snow and glacial ice. The peaks and higher slopes were denuded of their forests, and reduced, upon the disappearance of the ice, to a desolate expanse of dazzling white granite and glaring schists.
For at least the last thousand years, the Sierra Nevada has stood as it is to-day, a wonderland of high rugged mountains, deep mysterious canyons, and glacier-scoured ridges, covered in their lower reaches with oak groves or chaparral thickets, their middle slopes set with sombre giant pines and sequoias, and their sum mits marked by storm-scarred dwarf pines. The longer, gentler slope is toward the west, averaging about 200 ft. to the mile ; the
eastern slope is very steep, at its highest point above the valley opposite Owens lake dropping io,000 ft. in a distance of to miles. Few passes cross the range, Kearsarge and Truckee being the most celebrated. The highest part of the range lies between 36° 3o' and 37° 3o' N. lat. and here the peaks range from 13,00o ft. to 14,502 ft., the latter being the altitude of Mt. Whitney, the highest peak of the range; and all the passes are about 12,000 ft. high. Eleven peaks in the range are above 14,00o feet. From Mt. Whitney the elevation of the range gradually diminishes northward. The pre cipitation on the foot-hills and lower slopes is relatively light but with altitude it increases rapidly, most of it falling as heavy snow, particularly on the summits, which thus become store houses of moisture for irrigation and potable waters to supply power, agricultural and domestic needs of the population of the California valleys and coast.
Three main forest belts cover the flanks of the Sierra; the lower or main pine belt with sugar pine, yellow pine, Douglas spruce and incense cedar the dominant species ; the silver fir belt with the white silver fir (Abies concola), and the red fir (A. mag nifica) dominant species ; and the upper pine belt of tamarack, mountain pine, juniper, hemlock spruce, white pine, nut pine and needle pine dominant with altitude in the order named ; and finally at the summits the tangled dwarf pines showing not more than a foot of height or an inch of girth for a century's growth. The big trees (Sequoia gigantea) extend through the upper part of the lowest belt and the lower part of the middle belt. The foot hills and alluvial fans at the foot of the southern Sierras are characterized by Orion or nut pine, digger pine, blue oak and interior live oak, and an underbrush distinguished by the pungent manzanita, and the rude chamiso.
The fauna of the Sierra is characterized by the ubiquitous Douglas red squirrel, the mountain goat and mountain sheep; white-tailed, black-tailed and occasionally mule deer; grizzly, black, cinnamon and brown bears, now all rare; by representative birds like the Sierra junco, blue-fronted jay, the famous Clarke nut-cracker and others; and by distinctive mountain trout, like the rainbow and the golden. (W. E. E.)