I agree with imma, and would add Georgia to his list, based purely on historical, subjective, poor data set evidence of my own. I reflect on decades of travel and having lived in 3 states. I have seen Michigan, Texas, USC, ND and USC gear all around the country, consistently in up and down years for those programs. There is a big ND USC, and Ohio State presence in Nashville, Austin, Chicago and elsewhere. I don't really see Bama or Georgia stickers much outside the southeast, and sure as hell didn't when they were shitty. Sure, here and there you see those schools, but growing up, never.
Most people from CA that I know who don't have an actual team in the fight default to USC. In the Midwest and Northeast it seems most people pick between Michigan, OSU and ND for alumni or regional/personal reasons. None of those 3 seem to be limited to that region, particularly ND.
I'm curious and need to do/have a surly member research data regarding apparel/brand sales over the decades as I'm guessing that's a better measure of long term team allegiance and interest.