Insect gall, on creosote bush (Larrea tridentata), in Phoenix, Arizona. This gall is caused by the gall midge,

Asphondylia auripila. The brownish structures at the end of each whorl are the discarded pupal cases (exuvia) the tiny flies left when they emerged as adults. The entire gall is about the same diameter as a U.S. quarter (2.5 cm).