[Jcamper]

Generally speaking the difference between octane available in different areas relates to elevation, humidity, and temperature differences. Southern California is more hot/humid, so it needs a higher octane rating, while Colorado is at a very high elevation so you can get away with 85 octane there. Keep in mind that octane rating only rates resistance to "knock". Ethanol has a high octane rating, allowing jobbers (fuel wholesalers) to use a cheaper base fuel (less octane) when blending with ethanol to get the same overall octane rating for each load of fuel. However, ethanol also has less energy then straight gasoline, so a vehicle without modern O2 sensors and computer control will run leaner on oxygenated (ethanol added) fuel, which may contribute to poor running and pinging. Another issue is that ethanol evaporates extremely easily, making modern fuel much more sensitive to age. There can also be slight variations in what kind of mix you get one time to the next. When transporting fuel through a pipeline they run each type of product (straight, high, diesel) one after another, theoretically diverting the portions where they have mixed into a separate tank. Sometimes this doesn't get done perfectly. This sounds weird but it isn't a bad idea to sniff the nozzle before you stick it in your car, especially with a diesel pickup where the effect of having some gasoline mixed into your diesel can be extremely punitive. Sorry for the long post. Jcamper