Regardless of "coverage maps", cell phone use in Western states is something that should not be relied on! There are long stretches of highway out here, both interstate and federal highways, that cell coverage is spotty or non-existent.
Ham radio 2 meter and 70 centimeter repeaters, however, are very prevalent all across many states. Yes, you need a repeater directory, and your radio must be programmed to hit the repeater. Having a radio that has a SCAN feature to search for active repeaters is a plus. Getting an Amateur radio license is easy and inexpensive. The 2 meter/70 cm radios can be inexpensive or very expensive, your choice. The same goes for antennas.
Having a cell/smart phone can be nice, but in a life/death situation it could very well be worthless!
Why do I tout Ham Radio? Perhaps because I are one: KJ7POE