[Ramius]

If the entire Western US was buried in ash ...

I think it's more likely that the Midwest and eastern U.S. would catch the most ash. The jet stream moves the air west-to-east. The west coast could actually end up without much damage.

[Aria]

The maps I saw indicated the Pacific Northwest, northern California and a good portion of coastal southern California will be ok.

Not so sure about the food supply. And the North Dakota oil fields would be under ash. Can't even imagine what a catastrophe this would be.