Following text from http://www.abocanyon.clara.net/Tehachapi_Pass.htm
Located between Bakersfield and Mojave, this tortuous defile through the Tehachapi mountains separating Northern and Southern California presents an unenviable challenge to men and machines. The route was opened in 1876 by Southern Pacific, and the Atchison, Topeka & Santa Fe acquired trackage rights in 1899. Leaving Bakersfield, trains face a grade of 1 in 40 for 50 miles to the summit near the small town of Tehachapi, then down 1 in 40 for 18 miles to Mojave, on the edge of the Mojave desert. About a third of the route is single track. Scenic highlight is the famous Tehachapi Loop at Walong, where the line loops over itself to gain an elevation of 77 feet in a relatively small space.