I found this tree by a pool in Austin. It was starting to get dark so some of these pictures didn't turn out well. The tree was probably about fifteen feet tall, not very obvious in the fifth picture. The mature seed pods didn't rattle and you can see why in the third picture. Each bean(?) was tightly sealed in its own compartment.
My cousin said that several years ago a disease swept through the area and killed a lot of oaks, some of them upwards of a hundred years old, and the land lord started planting so many trees in the area that there are more now than there were before. I took these pictures with my iPhone 5.