Do you remember “Bay” brand gasoline back then?
It was rumored to be made of byproducts of some Dow Chemical high volume batch process and was always the lowest cost gas.
I do recall seeing the “BAY’” signs at times (bottom photo at link), probably when my parents were taking the family on vacation from Detroit area to the U.P. and driving through smaller cities.
http://www.gassigns.org/bay.htm
I don’t recall any stations “downriver” from Detroit when I was a young driver.