Fuel octane levels

So, I'm driving through Utah & Wyoming in the wifes 4Runner and I go to this gas station and there's 4 levels of gas, 85, 87, 89, & 91. Does anyone know why they have different levels like this? I've never seen this in AZ before. Of course I didn't choose 85, I went with the usual of 87. Just thought maybe someone on here might know the answer.

 

maybe the 85 is due to a larger contingency of people running heavy equipment, larger more rugged engines?? agriculture? hmmm

 

i believe the 85 is a 15% ethanol blend. not sure, but i think this to be the case.

 

Hell, just going through southern idaho, its common to see just 85,87,89.

I feel bad using 89... Especially when i was pampered using 93, before the dipshits did some behind the scenes handshakes, and claimed "ethanol will reduce foreign oil dependance".

 

Lower octane fuels are required at higher altitudes. For example, 91 octane is the best gas we can buy in much of Colorado - a far cry from the 93-94 octane fuels I could get in the northeast.