Looking between the two 1972 photos again, it looks like the restroom near Wheel of Fortune was also expanded. I believe that was an expansion to the women's section, and today that restroom is considered Planet Snoopy. Would that be it?

Well, I posted this, and then it refreshed to the next page and I saw someone got it!!!!!  Way to go, Ty.  The guess at the new restrooms between Rivertown and Antique Autos was VERY close!  Yes, they were put up mid season in 1972.   But before they broke ground on that building, they found that they had to rush an expansion on the women's side of the restroom between Rivertown and HB land.  If you look at the pic I posted at the beginning of 1972 and the one from October 1972, you will see an extra cube on the back of it next to the small flume.  The men probably didn't even notice.  And of course, the city limits of Rivertown have moved south, so that building is no longer in Rivertown.   Also notice that during one of the weekends in April before we opened full time, they added the red theme color to the blacktop walkways!   You can see some of HB Land's green in the arbor and near the back of the restroom.