Alright, so the bone of this postulation is extremely unlikely, so much so that divine intervention isn't entirely out of the question. However, for the sake of the discussion, let's say that plausibility is somehow waived and everything that could go right does go right, but no actual Alien Space Bats.
The following happens:
The following happens:
- H.H. Sibley wins a decisive victory at Valverde. More accurately, Colonel Green manages to redirect the 4th Texas into a different section of the Union line, and instead of plowing into a Coloradoan line unit they smash through a militia regiment and manage to fight clear to the river. Green manages to follow this up and spark a route, which results in the capture of Fort Craig and the dispersal of its garrison.
- With Fort Craig reduced, more men are able to move northwards with the main force to Glorieta Pass. Because of this, the Confederate supply train remains intact, and Sibley can be reinforced by forces coming up the Rio Grande.
- Santa Fe then falls, and with guns, bullets and food looted from the city Sibley's army manages to cross the Rockies and advance on Denver and its gold reserves, catching the remaining Coloradoans while they are dispersed and defeating them piecemeal.
- Somehow, be it swarms of bandits, hostile Indians or the South Platte having apocalyptic floods, the gold in Denver isn't evacuated before Sibley reaches the city and takes it. Meanwhile, the California Column gets hit by a series of giant dust storms and is scattered in the desert with few survivors.
- Sibley sends some of the gold back east but uses the rest to hire a makeshift army of bandits, Mexican Republicans, filibusters and various native groups. This 'army' goes east, following the California Column's supply route towards the west coast.
- Somehow, the California militia is inept enough that Sibley manages to reach the goldfields of the eastern mountains and makes off with a crap ton of gold. This is probably the least realistic part, I have no idea how it could've been pulled off. Still, it doesn't break the laws of physics, so it's not completely ASB?
- After securing several thousand pounds of gold, Sibley then turns and flees southward, dodging past the many Union armies attempting to halt his overburdened and exhausted 'army'.
- Sibley then manages to escape across the border to Mexico, whence he reaches a neutral/Imperial port and get the gold onto French and British ships as Confederate credit, then makes his way back north to Confederate Arizona without getting attacked by the Mexicans.