Immediately west of Mallín Ahogado, 15 kilometers northwest of El Bolsón, a signed gravel road suitable only for 4WD vehicles drops steeply into the canyon of the Río Azul, which flows eastward out of the Andes before turning sharply south at the confluence with the Río Blanco.

Beyond the Arco Iris campground, where the road ends, two precarious pasarelas (pedestrian bridges) cross the rivers before the trail becomes an up-and-down hike that leads to a sheer-sided gorge. Here, beneath a sturdy log bridge, the spring runoff explodes like a cannon shot.

Just across the bridge, about 2.5 hours from the confluence, Refugio Cajón del Azul is open all year. Run by an English-speaking semi-hermit named Atilio who offers a free coffee, tea, or mate to every arrival, the refugio also offers camping (US$2.50 pp) and mattresses for overnighters (US$9 pp) in a communal dormitory. Though dark, the rustically comfortable refugio even has a water-driven turbine for electricity.

Most supplies arrive on horseback, though in summer and fall Atilio’s irrigated chacra provides fresh apples, cherries, peaches, plums, raspberries, and the like. The westbound trail continues another hour or more to Refugio El Retamal (elretamal [at] gmail [dot] com, US$9 pp).

An alternative northwesterly trail from the Arco Iris trailhead dead-ends at Refugio Dedo Gordo (US$7 pp), providing access to the summit of its namesake 2,065-meter summit. Before the final climb to Refugio Cajón del Azul, a new but poorly signed trail climbs steeply southward and then drops into the drainage of the Arroyo Teno and to Refugio Hielo Azul (hieloazul [at] elbolson [dot] com, US$10 pp bunks, US$4 pp camping) This route allows overnight hikers to loop back to El Bolsón.