This cache highlights the triumph over geology by man and
machine.
The Tehachapi Pass forms the geological boundary between the
southern portion of the Sierra Nevada Mountains and the Tehachapi
Mountains and connects the San Joaquin Valley with the Mojave
Desert. During prehistoric times, the pass was a large river
corridor connecting seas located in the afore mentioned areas,
similar to the Carquinez Strait in the Bay Area. Uplift
caused by earthquakes on the White Wolf and Garlock faults
eventually produced over 4,000 feet of vertical offset, and left
Tehachapi Valley separated from the seas which have now dried
up. Evidence of this ancient waterway can be seen in the
limestone deposits mined in the nearby Monolith mine. The
continual uplift of this pass was seen on July 21, 1952 when
Tehachapi was devastated by a magnitude 7.5 earthquake along the
White Wolf fault. Approximately 4 feet of vertical
displacement was measured at the surface as a result of this
earthquake.
In more recent times this offset has proved as a natural barrier
between Northern and Southern California. In 1860 this
barrier was drawn as part of the dividing line in a potential state
spilt between pro-Confederates in Southern California and pro-Union
supporters in the north portion of the state. Prior to the
Ridge Route crossing the Grapevine into the San Joaquin Valley in
the 1920s, the overland transportation of goods and people was
rather harrowing. To overcome this, in the 1870's the
Southern Pacific Railroad sought to link their rails in central
California to those in Southern California. Since
construction directly south through the Grapevine was impractical
due to the terrain, the Southern Pacific decided to go southeast to
Mojave, through the Tehachapi Pass. Three thousand Chinese
laborers were used to build the 28 mile rail line between
Bakersfield and Tehachapi Summit along with 18 tunnels, 10 bridges,
and several water towers between 1874 and 1876. Construction
from Bakersfield to Caliente was somewhat routine, but from that
point on the elevation going east rises quickly. From
Caliente to the summit (now the City of Tehachapi) the rise is
2,735 feet. The maximum grade permitted was 2.2%. By routing the
track alongside the slopes of the Tehachapi foothills, engineer
William Hood was able to get the line just to the east of Keene
were there was an apparently unsolvable problem. An increase
in elevation of nearly 77 feet was required, unattainable using
typical designs.
The problem was solved by constructing a unique loop.
Going southeasterly from Keene, a train first passes through an
entry tunnel. The track then does a complete counterclockwise
loop, passing over the entry tunnel before continuing
easterly. The loop is sized to have a length adequate to
achieve the needed gain in elevation. The result is a loop
3,799 foot long, with a typical diameter of about 1,210 feet.
By continuing to gain elevation throughout the loop, William Hood
was able to make up the needed elevation With modern freight
trains, often more than a mile long, the locomotive passes over (or
under, depending upon direction) the final cars of its own
train. The single-track line, essentially unchanged through
the years, remains in use today and accommodates an average of 36
freight trains per day.
Logging Requirements: Park near the posted coordinates,
read the two historical markers and analyze the rock formation
along the south side of the road and answer the following questions
in an email to me:
1) What type of igneous rock was cut through to accommodate this
rail loop?
2) Describe the rock south of the markers along the side of the
road.
3) What do you think will happen to the rail line in the future
with more uplift caused by earthquakes?
Logs that do not meet ALL 3 of the
above requirements will be deleted.
Due to all the visitors this site gets,
please be mindful of the traffic and keep an eye on
children.