A couple things here:
the little cactus beside the saguaro is a baby saguaro. I thought it was a small barrel cactus, but in fact it's growing up in the protection of the big one. Saguaro can live for 200 years or more! Can you see the holes in it? The birds drill in there for shade & water. We watched on during church one morning (several mornings, actually!) and he pulled out a little bit of the meat of the cactus, and tossed it, and then headed in for another beakful.