Field areas

The Southern Sierra Critical Zone Observatory has five major field areas for research on USDA Forest Service and National Parks Service lands. A unique feature of our sites is an intensive measurement program along an elevation transect that extends from the rain-dominated Central Valley through the snow-dominated higher elevations of the Sierra Nevada. This transect covers from oak grassland through mixed-conifer forest to the red fir subalpine.

© Southern Sierra Critical Zone Observatory


San Joaquin Experimental Range (405 m elevation)

513 mm/yr

The San Joaquin Experimental Range (SJER) research site is in the oak woodland foothills of the southern Sierra Nevada at 405 m elevation. The primary land use at the San Joaquin Experimental Range is cattle grazing.

Soaproot Saddle (1160 m elevation)

805 mm/yr

The Soaproot Saddle site is located within Ponderosa Pine forest at 1100 meters in elevation within the Sierra National Forest.

Providence Creek Headwater Catchments (1660 - 2117 m elevation)

4.6 km2, 1660-2117 m elevation, 8 °C, 1200 mm/yr

The most intensively studied research area of the Southern Sierra Critical Zone Observatory is the Providence Creek headwaters area, located on the North Fork of the Kings River. The Providence Creek Headwater Catchments field area varies in elevation from 1660 to 2115 meters. This 4.6 square kilometer catchment is designated as P300. Nested within the P300 catchment are three subcatchments, designated as P301, P303 and P304.

Providence Creek Subcatchment P301

0.992 km2, 1790-2117 m elevation,

P301 Meadows

P301 Flux Tower (2015 m elevation)

1015 mm/yr

Critical Zone Tree 1

0.0001 km2,

Providence Creek Subcatchment P303

1.323 km2, 1731-2025 m elevation,

Providence Creek Subcatchment P304

0.487 km2, 1768-1983 m elevation,

Short Hair Creek (2700 m elevation)

1078 mm/yr

The Short Hair Creek field area in the subalpine belt of the Sierra Nevada. Due to harsh winter conditions and a falling tree, the flux tower was down from 2011-2014. A replacement tower was brought in by helicopter and raised by a team in August 2014. Instruments were reinstalled June 2015.

Wolverton Basin (2230 - 2700 m elevation)

8 km2, 2230-2700 m elevation,

The Southern Sierra CZO conducts additional research in the Wolverton basin, located at an elevation of 2230-2700 meters, in Sequoia National Park.

Flux Towers Transect

Transect area: 568 km2, 405-2700 m elevation,

The Southern Sierra CZO operates eddy co-variance flux towers installed at four different locations varying from 405-2700 meters.

Other instrumented sites

Other instrumented sites have been established in the Southern Sierra Nevada and are suitable for comparative research, including: Kings River Experimental Watersheds, Sierra Nevada Adaptive Management Project, and the American River Hydrologic Observatory.

Our Field Areas

Our Critical Zone Observatory has developed five long-term critical-zone research sites in areas operated by the USDA Forest Service and National Parks Service. Click on each to learn more.

The first four of our these listed sites form an elevational transect that increases in altitude from west to east. Along this transect, bedrock lithology is generally constant (intrusive felsic plutons) while air temperature, precipitation phase, biota species and abundance, and subsurface properties vary. A series of eddy-covariance gas flux towers are installed at these sites. Transect-length work has included soil depth, moisture, and biogeochemistry characterizations; vegetation surveys; forest water balance research; and wind-blown dust studies.

Subcatchment P301 of the Providence Creek Headwater Catchments area is the most intenstively monitored and studied area out of our five field sites. Recent research studies at P301 have included flux tower installation, several Critical Zone Trees, water balance measurement transect, geoprobe sampling and core characterization, bedrock geochemistry, active and passive geophysical studies, several soil pit characterizations, surface and subsurface hydrologic modeling, wind-blown dust analyses, and isotopic studies of snow, surface water, and groundwater.

The Providence Creek Headwater Catchments field area is co-located within the Kings River Experimental Watersheds (KREW) research landscape, operated by the USDA Forest Service Pacific Southwest Research Station. Four subcatchments comprise the Providence Creek headwaters: P301, P302, P303, and P304. KREW operates stream gaging and sediment basin monitoring in each subcatchment, along with two continuous meteorological stations in the field area. See the Other Instrumented Sites section below for more information.

We are currently developing a series of digital maps for our five research sites that will be launched in Summer 2018. Maps will spatially display current and previous core measurement locations and other research studies' sampling and measurement sites, along with available datasets.

Other Instrumented Sites

Additional instrumented sites have been established in the Southern Sierra and are suitable for comparative research:

Kings River Experimental Watersheds (KREW)
Kings River Experimental Watersheds (KREW) is a research program of the U.S. Forest Service, Pacific Southwest Research Station. KREW consists of two sets of four ~1-km2 headwater catchments, plus two larger catchments that encompass three headwater catchments each. The Southern Sierra Critical Zone Observatory is co-located with KREW at one of these areas, Providence Creek Catchments site. The second catchments site is located some miles to the southeast, approximately 400 m higher in elevation. These four ~1-km2 catchments comprise parts of the Bull Creek headwaters and the Teakettle Experimental Forest. Learn more on the KREW website.

Sierra Nevada Adaptive Management Project (SNAMP)
Data from two additional pairs of instrumented headwater catchments are available for comparative research, though measurements have stopped. One pair lies just north of the main CZO site, in the Sierra National Forest just south of Yosemite National Park. The second pair lies in the American River basin. There is also an east-west transect of instrumented sites in Yosemite National Park, along Tioga Pass Road. Read more about this project on the SNAMP website.

American River Hydrologic Observatory (ARHO)
Based on wireless-sensor measurement technology developed at the CZO, a basin-scale (> 2000 km2) observatory was developed in the American River basin. Twenty groups of wireless sensors similar to those in P301 were deployed to make representative measurements of snow properties and soil moisture across the landscape. Visit the ARHO website and the UC Water Security and Sustainability Research Initiative to learn more.

The Sierra Nevada

“Sierra Nevada” is Spanish for “snow-covered mountains”. This mountain range rises from near sea level, in the Central Valley, to over 14,000 feet at the spine of the range, which marks the edge of the Basin and Range Province in eastern California. Much of the ~650 km length and ~100 km width of the mountain range is underlain by plutonic igneous bedrock. Granites and granodiorites that formed approximately 120 to 85 million years ago are especially common near our Critical Zone Observatory’s field sites. However, extrusive, mafic, metamorphic, and sedimentary rocks are also found in the range.

The western slope of the Sierra Nevada is long and gentle compared to the short and steep escarpment found on the east side. This asymmetric shape is thought to be a result of uplift and tilting of the range by compressional and extensional geologic forces over the last several tens of million years. Glaciers have also left their mark, sculpting steep arêtes and deep cirques in the high country over the last two to three million years, during Pleistocene ice advances that were punctuated by ice free periods similar to our modern climate. Meanwhile, rivers have carved V-shaped canyons into lower elevations of the western slope, creating a landscape of broad interfluves and adjacent deep valleys. Our Critical Zone Observatory sites are located in this canyon country of the western slope, below the limits of recent ice advance.

Today the Sierra Nevada is drained by over 20 rivers and supplies about 60 percent of the water used by California’s agriculture, commercial industries, and residents. Annual precipitation in the Sierra today ranges from under one meter in the south to over two meters to the north, with a strong west-east gradient that increases with elevation. Along this altitudinal gradient, precipitation at lower elevations tends to be rain-dominated while higher elevations are snow-dominated. Air temperature also decreases as elevation increases.

Vegetation on the west slope closely reflects the variations in elevation and climate. Rising above agricultural lands of the Central Valley, grasslands merge into the oak woodlands that cover the western foothills in deciduous and live oaks, gray and foothill pines, California buckeyes, grasses, and chaparral shrubs such as ceanothus. These oak woodlands reach up to 600 m elevation in the northern Sierra Nevada and 1500 m in the southern part of the range. A zone of mixed-confer forests is found above this, comprising ponderosa and Jeffrey pine, incense cedar, white fir, sugar pine, and black oak. Mixed-conifer forests are found at elevations up to 2100-2700 m across the Sierra. Forests transition to lodgepole pine and red fir above this, with subalpine vegetation at the highest elevations.

MODIS image of the Sierra Nevada near peak snowpack, from its southern end to Lake Tahoe.