Introduction
The Onion Creek Experimental Forest was established in 1958 to develop techniques
for increasing water yields from forested lands in the Sierra Nevada snow zone.
Onion Creek encompasses about 1,200 ha in five main sub-basins. The aspect is
variable but generally southwest. Elevation ranges from 1,830 to 2,590 m. Harvest
disturbance is minimal. About 20 percent of the northwestern portion of Onion
Creek was harvested in the early 1900s and a portion of the forest is formally
withdrawn from mineral entry. Cattle grazing continues as nearly 200 cattle
pass through Onion Creek over a 3- to 4-day period twice each year.
Atmospheric deposition has not been measured on the forest itself. However,
annual hydrogen ion loading at the nearby Central Sierra Snow Laboratory of
the Pacific Southwest Research Station has ranged from 7 to 10 mg/m2 since 1983.
Mean annual sulfate ion loading since 983 is 4.5 g/m2 at the snow laboratory.
Climate
The climate is typically Mediterranean, with moist, relatively mild winters
and dry, warm summers. Annual precipitation is about 1,060 mm at 1,830 m elevation,
with 85 to 90 percent falling as snow during the winter. Mean monthly air temperatures
range from -1 °C in January to 15 °C in July. Monthly minimum temperatures
range from a low of -14 °C in January to 1 °C in July, whereas monthly
maximum temperatures range from about 13 °C in January to 30 °C in
July.
Soils
Mapped geologic units include Miocene pyroclastics with Andesitic mudflow breccias,
volcanic conglomerate, and some tuff. Quaternary glacial deposits include Pleistocene
moraines, glacial drift, and fluvioglacial sand and gravel. No mineralization
of economic significance is known to exist and no mining claims are recorded.
Soils are volcanic Xerumbrepts and have been classified as follows: Ahart/rock
outcrop (15 percent of the forest), Ahart/Waca (25), Gefo variate (5), Meiss
(5), Tallac (15) Waca/Meiss (5), Waca/Windy (5), miscellaneous (20). Cation
exchange capacities are 25 to 35 meq/100 g (sum of cations) or 20 to 30 meq/100
g (ammonium acetate). A soil resource inventory map (third-order soil survey)
is available.
Vegetation
The main plant communities are red fir (SAF 207), white fir (SAF 211), Jeffrey
pine (SAF 247), and dry meadow. An ecological survey of a portion of Onion Creek
listed major forest plant species including red and white fir, sugar, Jeffrey,
western white, and lodgepole pine, incensecedar, mountain hemlock, and western
juniper.
Long-Term Data Bases
Climatic data bases include air temperature, relative humidity, and precipitation
(continuous strip chart) since 1976; coverage before 1976 is sporadic. Hydrologic
data bases include continuous stream discharge records available from five sub-basins
with areas ranging from 0.5 to 2.1 km2. A sixth gauging station monitors the
entire 9.3-km2 basin. Snowpack depth and its water equivalent have been monitored
monthly at a snow course since 1937.
Research, Past and Present
Past research at Onion Creek dealt with the relationship of Sierra Nevada snow
dynamics to the red fir-white fir ecotone and also involved the use of meterological
and streamflow data to develop and calibrate rain-on-snow models. There is no
current active Forest Service research and the facility is now managed by the
University of California at Berkeley.
Major Research Accomplishments and Effects on Management
Topics of major accomplishments at Onion Creek include:
- Snow hydrology
- Freshwater aquatic biology
- Materials evaluation (weatherability of outdoor sign material)
Collaborators
Collaborators include scientists from the University of California at Davis
(mid-1980s), University of California at Berkeley (present), and California
Department of Water Resources.
Research Opportunities
Onion Creek offers an instrumented watershed with available historic climatic
and hydrologic data, and pristine forest conditions with limited roading and
historic management actions.
Facilities
Onion Creek is in the north drainage of the American River about 30 km west
of Truckee, California, on the Tahoe National Forest. Facilities are minimal:
one cabin with bunk beds for four and an outbuilding; no drinking water. Main
access is along 6.5 km of poorly graded county road. Commercial accommodations
are available 11 km away at Soda Springs. The Central Sierra Snow Laboratory
is located 11 km distant.
Lat. 39° 17´ N, long. 120° 21´ 15´´ W
Contact Information
Onion Creek Experimental Forest
USDA Forest Service
Pacific Southwest Research Station
PO Box 245
Berkeley, CA 94701
Tel: (415) 559-6316
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