The Sierra Nevada mountain range separates the Great Basin from the Great Central Valley. This mountain range has uplifted twice in its history; first as a result of the lifting of marine sediments and after millions of years of erosion, again mostly as a granitic mountain. These two uplift episodes were a result of plate tectonics. The extinct Farallon Plate was subducted under the North American plate as a result of eastward pressure by the Pacific Plate. This force did two things it lifted the ocean basin to expose the sedimentary rock to great heights (some estimate this height to be greater than today’s mountains) and the magma produced by the subduction created the granitic batholith that is today’s modern Sierra Nevada range. The point of contact of magma with the overlying rock resulted in transformation of the marine sedimentary rock into metasedimentary rock that is referred to as roof pendant. These roof pendants are the reddish fractured rock that is occasionally encountered in travels around the Kern River Valley.

The modern Sierra is aged at 2 to 40 million years of age depending on which geologist you ask. The Kern River Basin is uplifting at a steady 5mm per year.

There are multiple plutons that make up the entire batholith which were uplifted and exposed at different times throughout the entire stretch of the Sierra Nevada. The South Fork Kern River at its northern reaches is made up of intrusive (granite) and extrusive (lava) material near the Golden Trout Volcanic field. It drops rapidly from Inyo National Forest through granitic canyons into the Domeland Wilderness of the Sequoia National Forest and Bureau of Land Management. Although intrusive material makes up the bulk of the rock throughout the entire reach of the river, there are also noticeable areas of metasedimentary rock outcrops and limestone dikes in the lower reaches. Above Fay Canyon in Bartolas Country there are also five exposed outcrops of ancient volcanic basalt.

Granite is quite erosive and supplies the South Fork with a good load of sediment. The construction of Isabella Reservoir in 1953 cut off a significant portion of the sediment supply to the downstream portion of the Kern River. This has resulted in an increased volume of transportable materials deposited upstream of the reservoir due to reduced flow along through the South Fork river channel, increasing the potential for flooding throughout the South Fork Kern riparian forest.

Seismic Potential

The Kern River Valley is bounded by several major earthquake faults. The closest fault, Kern Canyon along the North Fork of the Kern River to Engineers Point between the main and auxiliary dams, was described until recently as seismically inactive. Research done by scientists at Caltech have discovered it to be a vertical slip fault that has moved more recently than previously thought. There are several local active faults capable of producing earthquakes that exceed magnitude 6.5.

Large earthquakes jolt the area relatively infrequently but regional fault zones have produced devastating earthquakes in the past. The White Wolf fault which runs along the southeastern edge of the San Joaquin Valley and is 60 miles to the west produced a magnitude 7.2 earthquake in 1952. This earthquake damaged Isabella Dam, then under construction, causing completion to be delayed by several months. The White Wolf fault along with the Garlock Fault just to the south delineates the horst (uplifted area) that makes up the Tehachapi Mountains. The White Wolf fault is the geological dividing line between the Tehachapi’s and the Sierra Nevada. The Owens Valley fault near Lone Pine east of Mt. Whitney separates the eastern Sierra Nevada from the Great Basin range. In 1872, it produced a large earthquake estimated at greater than 8.0 and actually lifted the Sierra Nevada 16 feet in some places.

Two other major faults in the region that are capable of producing massive seismic events have been relatively senescent for over 150 years, the San Andreas lies 100 miles to the west and southwest and the Garlock fault lies 70 miles to the south. The last major earthquake produced on the section of the San Andreas affecting our regions was in 1857. The Fort Tejon earthquake was estimated to be 7+ on the Richter scale.

Liquefaction is possible along the South Fork Kern. Groundwater in the South Fork Valley is relatively high which increases the risk for unconsolidated soils to liquefy as a result of a major earthquake. Groundwater is found at depths of 2 to 20 feet under the lowland areas of the Kern River Preserve.

Soils

Quaternary alluvium is extensive in Kelso and South Fork Valleys. The mostly sandy loam soil is a result of sedimentation from the flowing river. The soils that form the alluvial basin and the upland slopes are mostly from decomposed granite bedrock with limited metamorphic rock.

About Audubon Kern River Preserve

The Kern River Preserve is managed by Audubon California for the preservation of one of California’s largest contiguous cottonwood-willow riparian forests and the wildlife it supports.

Audubon Kern River Preserve supporters provide financial and volunteer support for Preserve outreach, education, wildlife habitat protection & stewardship.