I was looking on YouTube at train video and I found this very nice video of the Tehachapi Loop. The Tehachapi Loop helps get trains into the central California valley from the Mojave desert.
I have a link to a Google map of the loop so that you can see where it is located. this will give you an appreciation of the engineering of the railroad. I have driven through this area, but I have never taken the time to get off the highway to inspect the loop.