I searched for an hour at least...finally tried again the next day and asked the ladies in the Welcome Center about the gravel road and dumpster (so as not to give anything away). They said that the rest stop has been worked on and neither of these are there anymore. A geocache used to be there, but is also gone. I think there has been too much revision or construction to the place. So sad!

Rest stop has been moved 4-5 miles east about year ago, park attendant said. No trees anywhere in back. All plowed field. Nice welcome center, but box gone.

Couldn't find it. It looks like things may be a little different than from when you planted. I have pictures if you want to see them.