The Tehachapi Loop is a .73 miles (1.17 km) long 'spiral', or helix, on the Union Pacific Railroad line through Tehachapi Pass, of the Tehachapi Mountains in Kern County, south-central California. The railroad line connects Bakersfield in the San Joaquin Valley to Mojave in the Mojave Desert.
One of the greatest engineering feats of its day, the Loop was built by the Southern Pacific Railroad beginning in 1874. The first train to use it reached Los Angeles in 1876.
The Loop became the property of the Union Pacific in 1996, when it absorbed the Southern Pacific. Trains of the BNSF Railway also use the loop under trackage rights. Today, the railway line, with almost 40 daily trains on average, is one of the busiest single-track mainlines in the world.
As of 2012, Union Pacific bars passenger trains from the line, which is preventing Amtrak's San Joaquin train from serving Los Angeles. One exception is the Coast Starlight, which uses the line as a detour if its normal route is closed.
The Loop takes its name from its circuitous route, in which the track passes over itself, a design which lessens the grade. The loop gains a total of 77 feet (23.5 m) in elevation as the track ascends at a sustained 2% grade. A train more than 4,000 feet (1.2 km) long (about 85 boxcars) thus passes over itself going around the loop.
Notable contributors to the project's construction include Arthur De Wint Foote and the project's chief engineer, William Hood.
The location of the loop is known as Walong, named in honor of Southern Pacific District Roadmaster W. A. Long. The loop contains a siding, known as Walong Siding . It passes through Tunnel 9, the ninth tunnel built as the railroad worked from Bakersfield.
A large white cross has been placed in the center of the loop, at the peak of the hill. Known as "The Cross at the Loop", it is in memory of two Southern Pacific Railroad employees who were killed in a train derailment on May 12, 1989 in San Bernardino, California.
The Loop is today one of the prime railfan areas in the country with its combination of frequent train traffic and spectacular scenery. A railroad museum displaying related relics stands in the nearby town of Tehachapi. In 1998, the Loop was named a National Historic Civil Engineering Landmark. The site is also now registered as California Historical Landmark #508.