Argentina Guide
Mendoza, San Juan and La Rioja
Reserva Provincial Laguna Diamante
Some 220km southwest of Mendoza, LAGUNA DIAMANTE, set amid its own provincial reserve of guanaco pasture and misty valleys, is the destination of one of the least-known but most unforgettable excursions in the area. The source of the Río Diamante, which flows through San Rafael, the lake is so called because the choppy surface of its crystalline waters suggests a rough diamond. One reason for its relative obscurity is that weather conditions make it possible to reach Laguna Diamante only from mid-December to the end of March, with blizzards often blocking the road for the rest of the year. At Pareditas, 125km south of Mendoza by RN-40, take the RP-101, which forks off to the southwest; the drive down is one marvellous long panoramic view of the Andean precordillera. The RP-101 is a reliable unsealed road that follows Arroyo Yaucha through fields of gorse-like jarilla and gnarled chañares, affording views of the rounded summits of the frontal cordillera, before entering the Cañón del Gateado, through which the salmon-rich Arroyo Rosario flows past dangling willows. At another fork in the road, 20km on, the track to the left eventually leads to El Sosneado, while the right fork heads for the Refugio Militar General Alvarado, the entrance to the Reserva Provincial Laguna Diamante.
The place is so remote that there's no public transport out here – you need a 4WD – and few tour agencies offer the trip; try Argentina Mountain, at Lavalle 606, San Jose, in Guaymallén, Mendoza ( 
0261/4318356, 
www.lagunadeldiamante.com ), which offers day-trips from Mendoza as well as longer horse treks and climbs up Maipo and Tupungato. You may also be able to pick up a tour from San Rafael, which is closer in distance. Since it's in an area under military control, near a strategic point on the Chilean border, take your passport.