I'm not sure what this kind of tree is, but if you split open the seed pods you will get very sticky!
We discovered that we were pretty clueless about the types of trees at this park. I think next time we will bring home some leaves and try to identify them with the guide I found on the Arbor Day Foundation website. (J. Sterling Morton is the Father of Arbor Day, fyi. I am full of all sorts of Nebraska trivia since I had to review my fifth graders for the Nebraska history tests.)