So looks like they went with 5 year rotations.
Everybody plays everybody at least 2 times in 5 years.
The most you can play a unprotected rival is 3 times in 5 years.
Oregon and Wash are protected rivals that will play every year.
But Wash or Ore are not protected rivals with USC or UCLA.
So since Iowa has 3 protected rivals, They will only play 2 other teams (NW and MSU) 3 times in 5 years
But since PSU has no rivals, it will play 11 different teams 3 times in 5 years.