I would ask the rangers first. But, when I hiked enchanted rock, I just kept the food in the tent with me. There aren't any big predators to worry about (well there are occasional cougars, and coyotes, along with lots of people).

Incidentally, for all those interested. If you plan a backpacking trip to Enchanted Rock with your brother in law, and then your wife schedules an ultrasound for your second child to happen during the trip, it is always better to cancel the trip than to hear about not going to the ultrasound for the rest of your life. Apparently "I already saw the first kid, why would the second look different" is not the right answer.