The parks were indeed identical, same rides, same shows, everything. Marriott wanted to, besically, be the McDonald's of the theme park industry by building identical parks across the country. The idea was, guests could visit a Great America park wherever they were and would know what to find, where. No surprises. They never got any further towards that goal than some planning for the DC area park.
It only took a few seasons for Marriott Corp to drop the idea of completely identical parks in favor of giving each park unique, and thus promotable, attractions. The American Eagle was built at the Chicago park for that reason, I forget what the California park got.
Marriott later decided to get out of the theme park business entirely, I want to say this was in the early 80s but I'm not sure. The Chicago park was sold to Six Flags Corp (I think Six Flags was owned by Bally's back then, but I'm not sure). Marriott had obtained the license to the Warner Bros characters for the Great American parks, so it was this sale that led to Six Flags holding the license for the characters.
The California park was sold to a company that wanted to raze it and build a housing development, but the city government stepped in and took over the park to stop that; they wanted to keep the tourist dollars flowing in. They hired Kings Entertainment to manage the park, and KECO later bought it as noted in Rob's post.
My. Sorry to go on, I'm at work and it's slow!
-------------
Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read.
--Groucho Marx