Atomic Breakers had no removable pieces and was filled in with dirt. Lemon Drop and Peppermint Twist were removed permanently but parks have a tendency to hold on to slides like these on the off chance they can be sold for some sort of money. Fibreglass is not scrapable so WCusa stands little chance of making any money by sending them to the scrap heap.
After looking at Google Maps History where there are images without foliage completely blocking that area, I found that it really isn't a boneyard. It looks like a building of some sorts, probably like an office for WCUSA executives. There are also cars visible in that area, so an office of some sorts seems a lot more plausible than a boneyard. However, there might be some sort of storage there too, but I don't really think it's a boneyard.