Tehachapi was built by the Southern Pacific in the 1870's as a route to get from Southern California to the Bay Area. The Santa Fe and Southern Pacific entered a joint agreement to operate the line around 1899. Leaving Bakersfield, the tracks ascend a 2.2% grade until they reach the town of Tehachapi. Working their way up or down, trains pass through numerous horseshoe curves, the most spectacular of which is at Caliente and several tunnels, eventually reaching the famed Tehachapi Loop. Trains that are long enough will pass over themselves (and most trains do) as the tracks pass as the lower part of the train comes out of Tunnel 9. At one time, there were a total of 18 tunnels on the route, but a 1952 earthquake resulted in the daylighting of some tunnels, and line relocations and improvments have also bypassed a few tunnels. The longest tunnel on the line is Tunnel 5 at Cliff.

Today, the train frequency is about 60-70 trains in a 24 hour period, making it one of the busiest single-track railroads in the world. From my own observations over the years, BNSF tends to run more trains during the day than UP does. Traffic for both railroads is a mixture of intermodal and general merchandise.

If you decide to pay a visit to Tehachapi, you should at least be able to find the Loop, as directions off of the main highway point you right to it. Other locations I also highly recommend are Caliente, Tunnel 2, Bealville, Cliff, and Monolith. A railmap should show you where these locations are. Tehachapi is best visited in early spring when the weather is quite pleasant and the hills are still very green. Tehachapi is the a mecca for railfans from all over the world and I higly recommend a visit.