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University of California Publications in Botany
University of California Publications in Botany Author:University of California (System) Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: as passes, as Donner Pass, Tioga Pass. These places where the continuity of the summit region is interrupted are numerous but to only a few can much significance... more » be reasonably ascribed as barriers to plant invasion from the north. The first depression which seems significant is that through which the railroad passes from Sacramento to Truckee (Donner Pass, 7,000 feet); a number of forms present in the northern Sierra do not appear to the southward. The second of these possibly significant depressions occurs about 120 miles to the southeast, intersecting the summit east of Yosemite Valley; Tioga Pass, 9,941 feet, breaks the continuity of the arctic-alpine life-zone for a distance of about three miles. The last gap reasonably to be considered as effective in this connection is some 25 miles southeast of Tioga Pass. This last pass has not been visited by me but Professor J. N. Le Conte describes32 the High Sierra breaking down completely at Mammoth Pass (9,350 feet), where the crest consists of rolling hills and the forest belt crosses the range for a space of 20 miles. CLIMATOLOGY CLIMATE OF THE SIERRA NEVADA The data bearing upon the climate of the higher Sierra, and especially of the region included within the limits of this report, are still so fragmentary that only general statements are warranted. The section across the range, through which the Central Pacific Railroad passes, has been longest studied and its central position permits certain general conclusions to be drawn concerning the climate of the Sierra as a whole. In very recent years there has been an increasing interest in the climate of the California mountains and numerous stations of record have been established. The climate of the Sierra is conditioned by its northwest-southeast trend across the track of ...« less