A guided tour of the spring and watershed area next to the Arizona/Mexico border includes the human history and culture of the region as well as its geology and wildlife, from 7:45 a.m. to noon, Friday, March 14; free. Youth must be at least age 12 and accompanied by an adult. The walk will last about two hours over uneven ground. Call (520) 387-6849, ext. 7302 for reservations.