And I'm not so sure about coastal Northern California / Southern Oregon. It's marked on the map as being not that difficult. But I believe there are still plenty of paranoid, heavily-armed pot growers up in that area.

To get to Colorado means getting past Mormons, the cartel, machine gun enthusiasts, armed farmers, and backcountry hunters(militia should also be a concern in that area). Colorado is quite well defended by topography and neighbors that they might as well just stay high and chill.

Coloradans are fit, enjoy difficult hunting in bad terrain, know how to maneuver off road vehicles, are naturally trained at high altitudes, generally have good survival skills, and includes a large population of active or former military.

Not to mention, the Rockies stretch the entire length of the State.

They're a good candidate for the Final Boss.