The expansion-era Astros and Oilers both played at the Houston Astrodome
How are things on the West Coast?
In 1952, none of the leagues had more than 16 teams, and only the NFL had one west of the Rocky Mountains.
Due to a wave of moves and expansion in the 1960s, a wave that continued into the 1990s, we began to see teams in western and southern markets such as Los Angeles, San Francisco, Atlanta, Miami, Tampa, Phoenix, Denver and Seattle. Each league has 30 or more clubs, with at least five of them in the western United States.
Part of this was due to the fact that each of the Big Four pro leagues had a competitor that forced expansion into smaller markets: the NBA and the ABA, the NFL and the AFL, the NHL and the WHA, even MLB and the Continental League, which never played a game but still forced the creation of the Mets, Twins, Astros and Angels.