Believe it or not let's start with the one team that brings the region together every Fall, the Dallas Cowboys. Outside of Greater Houston the entire rest of the state is primarily Cowboys Country while Cowboys Nation extends deeply in to Oklahoma as well except for the Northeast corner that skews more towards the rams or the Oklahoma Panhandle which might lean to the Broncos. The average citizen on the street in Oklahoma will tell you they want nothing to do with anything coming out of Texas but bleed blue in spite of their pronunciations at least from September to January.
Where the splintering begins remains in the game of football, however, at the collegiate level where Dallas becomes the epicenter of the rivalry between the Texas Longhorns of Austin and the Oklahoma Sooners of Norman . There is no strong professional baseball rivalry since the Rangers are the only team along I-35 until you get to Kansas City. Uh...no real rivalry there at the moment. Things heat up for basketball, though, which probably is the showcase sport of contention for the region.
The San Antonio Spurs really get under the skin of Dallas Mavericks fans while there is no love lost in the other direction either. The gleeful thing for "Mavs" fans this season is that San Antonio was eliminated from the 2011 playoffs. The irony of it all is that the Mavs are now locking horns with, of all cities, the Oklahoma City Thunder, late of - wait for it - Vancouver, Canada! It's too early to call it a conspiracy but if Dallas wins the Oklahomans will have one more reason to loudly pronounce their hatred of all things below ("beneath" to some folks) the Red River. At the same time, if the Thunder win the semis to advance to the Finals the tune won't change a whole lot from the former scenario.
If I look at I-5, the backbone of California and the West Coast I'd see a more clearly defined landscape. With the exception of Los Angeles not having a football team each major city has its own set of football, baseball and basketball teams to celebrate, from San Diego to Seattle. Likewise I-95 running the Eastern Seaboard of the country; to each his own in every major city from Miami to Boston or even I-80 from New York to San Francisco. There truly doesn't appear to be anything like the I-35 Rivalry anywhere else in the country.
It happens. Enemies gather in Dallas in October for "Texas-OU Weekend," formerly held at the Cotton Bowl downtown but now played in Arlington at Cowboys Stadium. They do battle on Saturday and then return the next day to the exact same venue proudly wearing and swearing by the Silver and Blue! Whaddya gonna do?
Only thing anyone on the RIGHT side of the Red River would do: Go Mavs!!!