On a holiday road trip to California, I took some snapshots of some of the gas stations along the way to see the differences in gas from here in Tucson, which was $3.28 at the Shell gas station on Valencia Road and 12th Avenue, to Whittier.
And here is a trip to Southern California in gas prices:

In Picacho Peak, on Picacho Peak Road, this Shell gas station is $3.59 per gallon, however the Shell gas station across the street offered a different price.

Hundreds of yards away, this Shell gas station is $3.69 per gallon, 10 whole cents more expensive than the same company's station across the street.

In Eloy, the gas prices dropped slightly to $3.47 per gallon.

In Casa Grande, the gas prices at Love's gas station dropped to $3.29 per gallon.

Across the Interstate from Love's, at the Petro gas station, gas prices are $3.33 per gallon.

In Maricopa County, off of exit 151 at a small truck stop gas station, gas prices are up over 20 cents at $3.59 per gallon.

In Gila Bend, off of exit 119, the Shell gas station offers gas at $3.59.

In Buckeye, at another Shell gas station, gas drops to $3.45 per gallon.

In Quartzite, off of exit 17, at Pilot travel gas station gas prices drop slightly before crossing the border to $3.39 per gallon.

Across the border and into California, the Mobil and Shell gas stations offer gas at $3.89 per gallon; 50 cents more than the last gas station in Arizona.

In Banning, off of exit 17 at the Chevron gas station, gas goes up six cents at $3.95 per gallon.

Once in Whittier, the Mobil gas station sells gas at $3.71 per gallon, 24 cents lower than off the traveling freeway.

Across the street from the Mobil gas station, however, is an Arco gas station offering gas for $3.49, the lowest gas price I saw for the rest of the trip.
After four days, the gas prices at the Valencia Road and 12th Avenue Shell gas station back in Tucson dropped three cents.