Try most Costcos (at least in the northern part of California...except the northwest coast)). It is $4.37 a gallon for 87 grade at Costco in Concord, CA.
Costco in San Luis Obispo is $4.39 a gallon.
Not trying to shill for Costco, but if anyone is not a member, it is worth the low cost of membership for just the gas savings alone. Plus, it is "Top Tier" gas, unlike Sam's Club, Walmart. or BJ's Wholesale Club, for example.