CENOZOIC HISTORY OF THE KERN RIVER, SOUTHERN SIERRA NEVADA MOUNTAINS

The Kern River is the only major, south-flowing river in the Sierra Nevada Mountains of California. Currently it extends 130 km southward from near Mount Whitney and then turns southwest for another 80 km to its terminus in the southwestern end of the San Joaquin Valley. It has a drainage area of about 2500 miles². The river transports a variable yearly volume with a mean of 7 x 10⁵ acre feet/year (44 year record). This new study delineates the various courses of the river over the last ~80 my, based on deposited sediments and canyon morphology. The sedimentary rocks in the southern San Joaquin Valley have been extensively drilled during petroleum exploration and provide age markers for the past 22 my.

From ~80 to 22 my, the upper (36.69^o to 36.25^o N Lat.) and middle (36.25^o to 35.67^o N Lat.) parts of the river occupied its present course; the lower course turned eastward at Lake Isabella to probably join the early Colorado River. This particular course is dated from sedimentary rock in the El Paso Basin on the east side of the Sierras.

At 22 my, the upper and middle parts of the drainage were separated by a fault near 36.25^o N. From 22 to 12 my, the river flowed along the middle and lower courses only, and it turned westward at about 35.33^o N to flow into the southern most part of the San Joaquin Valley. This course is documented by the Bena sedimentary rocks.

At 12 my, the lower course was interrupted by faulting and by tilting of the Walker-Isabella block 1-2^o to the northwest. This river course fed into Ancient Lake Isabella and occupied its present lower course. Stevens and Kern-Chanac sedimentary rocks document the history of the Kern River for the past 12 my.

At about 9 my, the upper and middle courses were reconnected by tilting of the central-northern block of the Sierras. The river continued to flow into Ancient Lake Isabella, and with the increase of discharge associated with the Ice Ages, the river incised the natural dam and drained the lake.

Determining the changes in the river appears to be the key to understanding and dating the tectonic events affecting the entire southern Sierra block—planned as the next step in this study.