That's not EXACTLY true. The Pacific Coast Conference cracked up after the 1958 season with Cal, Stanford, UCLA, USC, and Washington leaving and over the next few years let the other three back in and they really only let them back in because the proposed Airplane Conference that would include those five didn't get off the ground.
So three of the five who formed the second big time western conference in hopes of joining a cross-national conference in 1959 got their wish this year in joining Big 10 along with Oregon and the other two got their wish by joining ACC.
Meanwhile Arizona and Arizona State get rejoin their old Border Conference foes Texas Tech. Old Skyline members Utah, BYU and Colorado get back together as well.
Sometimes you break up and get back together.