I've tried to spend some (admittedly limited) time researching the title topic, but have come up short. Everything I've found refers to the area around Tennessee, Missouri, Mississippi and Alabama as the "Western Theatre", but I am more specifically interested in the area west of the Rockies.

Was this area of North America affected by the Civil War in any great regard? Or did the geographic distance cause it to be thought of as more of "their" problem (in regards to the East Coast of the continent). California and Oregon had already been admitted to the Union by this time, so I can't imagine it was possible to stay "neutral", so to speak.

Any info anyone has would be greatly appreciated, especially sources to follow up with so I can do some additional reading!