These are by far the coolest galls I’ve ever seen! I spotted them on the leaves of some Sonoran Scrub Oak at the top of Tom’s Thumb Trail. In checking BugGuide on the net, the most likely candidate for creating this gall is a Gall Wasp. If anyone has an idea of the exact identity of this gall, please let me know and I’ll post the ID. Thanks!

The largest gall measured approximately five eights of an inch.