Nevermind about my Page, AZ guess. I checked Sonic's official site, no locations in Page. Guess that drive-in place in Page was an A&W after all.
BUT, theres a good chance they were in Flagstaff. Looks like there are quite a few Sonic's around there.
So, now another guess, they are going to Petrified Forest National Park to look at 2000 year old hard wood