I took a trip to Death Valley last spring. I spent about a month of my spare time to figure out all the frequencies I would need to have programmed to get all the traffic.
In the park itself, there is really only one active channel (the park's frequency). The CHP in the park, and around in California are on Gold. Don't forget you need two frequencies programmed and a good antenna to pick them up.
Nevada was a tough one to program in advance because it is all 800 MHz EDACS. There are a lot of repeaters and a lot of driving distance between many of them. The repeater you will get the best signal from is not always the closest one. If you are using an object oriented scanner, I don't think it would be much of an issue. But I had to use all 10 banks of my bank oriented scanners to program in enough sites, and then re-programmed them every few hours as I made my way from one area to the next.