Rock-Ice Feature Inventory for the Sierra Nevada, California, USA
The Sierra Nevada is a tectonic uplift mountain range with a gradual gain in elevation on the west side and a steep escarpment on the east. Most of the mapped locations are east of the Sierran crest. The climate in the region is Mediterranean, with most of the precipitation in the winter months coming as snow at high elevations, but with some monsoonal precipitation in the summer, particularly in the southern end of the range. There is a very steep gradient in decreasing precipitation eastward from the Sierran crest as a result of rain-shadow orographic effects from the predominately eastward-moving Pacific frontal storms. PRISM-estimated (Daly et al. 1994) annual precipitation for the RIF locations ranged from 580 to 1880 mm; July precipitation from 5 to 33 mm. Mean annual maximum temperatures ranged from 1.8 to 15.2 oC, January from -5.7 to 6.2 oC, and July from 11 to 26.3 oC. Mean annual minima ranged from -8.1 to -0.4 oC, January from -15 to -7 oC, and July from 1.2 to 8.9 oC. The highest temperatures and lowest precipitation were largely at relict Pleistocene rock glaciers, which tended to be farthest east of the Sierran crest and lower in elevation. We mapped over 430 RIFs, based on field surveys and grouped them into six classes based on morphology and location. These categories constitute a greater range of frozen-ground features than are commonly described in rock-glacier surveys. Although granitic substrates dominate the Sierra Nevada, they do not in the eastern escarpment, so substrates in the RIF database are about equally divided between granitic and metamorphic. Ages of rock glaciers ranged from current (active) to relict (late Pleistocene). We interpreted the presence of outlet springs, basal lakes, suspended silt in outlet streams, and fringing phreatophytic vegetation, in addition to morphologic indications of current rock movement, as evidence for interstitial ice, either persistent or seasonal.
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Millar C. and R. Westfall. 2009. Rock-Ice Feature Inventory for the Sierra Nevada, California, USA. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center.