|Courtesy Wikipedia/Originial uploader was Slambo
The Tehachapi Pass Railroad Line was cut through solid and decomposed granite by about 3,000 Chinese laborers using nothing more than picks, shovels, horse drawn carts, and blasting powder. This line, which rises from the San Joaquin Valley and through the Tehachapi Mountains, originally included 18 tunnels, ten bridges and several water towers to accommodate the steam locomotives. Completed in less than two years, it was part of the final line of the first railroad to connect San Francisco with Los Angeles.
The single-track line, essentially unchanged through the years, remains in use today and accommodates an average of 36 freight trains per day. The Tehachapi Loop, which is about half way upgrade to the Tehachapi Pass, averages 2.2% in gradient across its 28-mile length. The unique loop provides an entry tunnel from which the track travels in a complete counterclockwise loop that passes over the tunnel. The loop is 3,799-feet long, with a diameter of about 1,210 feet.
John R. Signor, Tehachapi, Golden West Books, San Marino, CA, 1983.