I just got back from a two week trip south (at least south from here). Fuel prices varied from a low near 2.24-2.40/gal in Montana and Idaho, to a high of 3.18-3.65/gal in California (the 3.65 was in the Mount Shasta Park area.)
It was easy to find fuel for 2.50/gal in most areas of Montana, Idaho, Utah, Oregon and Wash. California was all over 3.00 that I saw.
Here in Cranbrook, price is 95.4/litre today (~3.09US/USgal)