The Tumacácori Highlands, northwest of Nogales , can best be accessed using exit 12 (Ruby Rd.) off I-19 just north of Nogales. West about 11 miles is Peña Blanca Lake, where bass and catfish can be lured in but not eaten because of high mercury content. There’s a boat ramp and trail around the lake.
Branch off on Forest Road 39 for the White Rock Campground, which has sites year-round, but no water ($5). Continue another five miles along Forest Road 39 to the trailhead for the Atascosa Lookout Trail. The popular steep trail to the 6,255-foot peak, a six-mile round-trip, takes you to a decommissioned fire lookout which, for a few months in 1968, was manned by writer Edward Abbey.
There’s a sign pointing to the trailhead for the Sycamore Canyon Trail on Forest Road 39 about 10 miles in from Peña Blanca Lake. This trail leads deep into a watered canyon, with steep walls dotted with saguaro, white sycamore trees, and jagged rocks jutting out from above. It’s a five-mile hike one-way to the U.S.-Mexico border, marked by a barbed-wire fence.
The trail isn’t always well marked, as the creek often overtakes it and you will certainly have to wade in parts. During the rainy season some sections may be impassable. The canyon is a major corridor for drug smuggling, and you are likely to see a lot of trash and other evidence of the trade.