While VHF/UHF repeater coverage in Colorado is excellent because most of the repeaters are on top of mountains, you can also find a lot of places in the back-country where you can't hit a repeater because some @#$%^ mountain is in the way
You could also communicate via satellite. There are ~20 amateur radio satellites currently operating.
Then there are the "traditional" methods using HF frequencies.
The Amateur Radio Relay League (the national ham group) runs an exercise annually that focuses on various modes of operating in the field. Hence the name, Field Day. Unfortunately, it was last month.
But the ARRL or a local ham club will be a better resource than random ramblings here. Check them out (or find a local club) at arrl.org.