Pacific Republic
I went with “other” for an economic reason.
At the outbreak of the war, Colonel (brevet Brigadier General) Albert Sidney Johnston, commanding the Department of the Pacific, co-operates in establishing the Pacific Republic, consisting of California and Oregon. The Pacific Republic is specifically distinct from the Confederate States of America, being founded on the cause of freedom and traditional popular sovereignty. Although much of the support for secession is from the “southern” population of California, slavery is not an issue. That decision had already been made. Isolation and general “cussedness” play their role.
Perhaps, the Californios see an opportunity to restore some of their standing. Maybe, Mariano Vallejo weighs in.
OTL, California had a very high per capita military participation. With that, Oregon might be subdued.
Nevada also had a substantial “southern” population, many of whom had come from California. Nevada could soon adhere to the Pacific Republic.
If successful in Oregon, the Pacific Republic might also acquire Washington Territory.
New Mexico Territory would be significantly harder to obtain, since the population centers were closer to Texas and more likely to be acquired by the Confederate States of America than the Pacific Republic.
The Latter Day Saint settlers of Utah, and other areas of the Great Basin and the other settler of the west at that time were often not on good terms, so adherence of the Latter Day Saints to the Pacific Republic would not be likely. If circumstances were to permit, they might establish their own nation.
The critical importance of the Pacific Republic is economic. If the California and Nevada components were quickly to be effective, regardless of what happens with Oregon, Washington, New Mexico, or Utah, the Union would be deprived of the resources of the Mother Lode and the Comstock. Some significant sinews of war would be severed.
Not that the Confederate States of America would succeed to those sinews. Overland transportation would be difficult. The Union navy could be expected to interdict sea transport. Some sort of financing scheme might be created, but, without good communications, would be difficult. And the interests of the two nations would co-incide only in part. The only gain for the Pacific Republic in subsidizing the Confederate States of America would be a greater likelihood of independence. With the secession of both groups of states, that might not be necessary.
Whatever the long run for the Pacific Republic, the Union is deprived of the resources of the Mother Lode and the Comstock.