Tehachapi Area Geology
The Tehachapi was covered by a vast, warm, shallow sea, like the Caribbean. The limestone mined here was formed during this time. The limestone was intruded by molten granitic rock, which at this location did not reach the surface as lava or volcanoes. The intruding granitic rock metamorphosed the limestone into marble which at places is mineralized with gold and tungsten. The suite of minerals formed by contact metamorphism was created by the contact of the molten rock with the limestone. The granitic rock and the limestone were tilted up, steeper on the east than the west. Erosion during this time removed nearly all of the marble, and generally the high places were made smooth. The summit of Cummings Mountain is nearly smooth, as is Bear Mountain, and there is a prominent erosional surface to the north of Tehachapi. Some of these high peaks have out-of-place river cobbles.
During the period of time that three-toed horses, saber tooth tigers, and mastodons wandered the area, Tehachapi Valley was a major river corridor, like the Carquinez Straits where the Sacramento River passes through the Coast Range. At that time, let us call it Tehachapi Strait, was the last connection between the ocean and the Mojave Desert. There are recent marine rocks in the El Paso Mountains, and there are plants and animals in the Southern San Joaquin Valley only found in the Mojave Desert. Perhaps an early, pre-Garlock fault cut through the Valley here. There are apparently inactive east-west faults which cut the base of the mountain south of the Nazarene Church, and just north of State Highway 202 from Jury Road to the small pass west of the Bear Valley entrance Station... which probably created Bear Valley. Movement on the White Wolf and Garlock faults uplifted the Tehachapi Valley and cut off the passage between the San Joaquin Valley and Mojave Desert. The river probably flowed through Tehachapi and Cummings Valley. The sand from this river system has been mined for winter road sand by Caltrans.
Increased uplift of the Sierra and Tehachapi Ranges was accompanied with intense volcanic activity north and within Sand Canyon. Volcanic ash layers and volcanic flows repeatedly covered the lush river-side environment. The volcanic ash layer is the source of silica for chert which the Indians made arrow heads. Also, the ash was altered by rainwater to form a very high purity, adsorptive clay. That was mined during the 1920s for oil purification. There is also abundant petrified wood found associated with the ash layers. Because of the highly variegated colors of the volcanic rock, it was mined at many places for roofing granules.
Uplift caused by earthquakes on the White Wolf Fault eventually produced over 3,000 feet of vertical offset, and left Tehachapi Valley separated from the San Joaquin. Finally Tehachapi Creek began cutting headward into Tehachapi Valley from the northwest. During this time large volumes of water flowed from the mountains to the south of Tehachapi. Evidence for this are numerous large drainages, including Brite Creek where it crosses Woodford-Tehachapi Road and two drainages which cross SR 202 between Sage and Golden Hills Boulevard.
Though no contemporary records exist, the valley must have been severely shaken by the 1857 quake on the San Andreas Fault. In the 1952 "Tehachapi Quake" structures throughout the valley were destroyed, and a number of lives were lost. The quake was generated by the White Wolf fault. Movement thrust Bear Mountain some three feet higher. The fault was named for a ranch which lies just south of Highway 58, just south of SR 223. The fault runs along the base of Bear Mountain and has created the steep escarpment that separates the Tehachapi Valley and the San Joaquin Valleys.
The Garlock Fault lies little more than 5 miles southeast of downtown Tehachapi. Though it probably hasn't experienced a significant earthquake in 1000 years it is capable of quakes of magnitude 8. This fault creates a startling and dramatic geologic, geographic and physiographic division. While rocks on opposite sides of the San Andreas have traveled farther, the physiographic contrast across the Garlock is more startling. To the south of the Garlock Fault, the Mojave Desert consists of subdued mountains, separated by great plains. To the north are a series of high north-south trending mountains, and deep valleys, including Death Valley. Most faults in the State run north to northwest. The Garlock primarily runs east-west until it hits the trace of the Sierra Nevada Fault at Red Rock Canyon, then it swings southwest until it intersects the San Andreas at Gorman.