The difference in Vapor Pressure for gasoline is often modified by the inclusion or exclusion of amounts of butane.
Different areas of the state likely have their own tank farms where the local recipe is blended. That is common elsewhere, but I have not designed/built gasoline/diesel tank farms & loading terminals in the Rocky Mountains where altitude changes rapidly with distance. I have in more flat land and that is common. What I have seen is the only different in most locations is the brand name additive.
However, I did that work when we mostly used MTBE and not so much since the ethanol push. I expect but do not know, that the ethanol is already blended into the large gasoline tank(s). To blend the ethanol per truck would require additional tanks(s) and pumps per facility from the previous designs.
Thanks.
In regard to ethanol content, I’m not positive, but I think the percentage of ethanol is consistent throughout the state, and everyone changes the percentage at the same time.