Embalse El Yeso is a reservoir in the high Andes, an hour or two above the last village of the Cajón del Maipo, and its colour alone is enough to make riders brake. The water is a shade of turquoise that seems artificial, held in a bowl of bare brown mountains with snow patches on the heights and the cone of Volcán San José standing guard at nearly six thousand metres. The dam was built in the 1960s to supply drinking water to Santiago, and the lake is still a vital source for the capital, which is why access is controlled and swimming is not allowed.
The approach is half the pleasure. From San José de Maipo, the road follows the river upstream through a narrowing canyon, past little settlements, orchards and hot-spring resorts, with steep walls of red and ochre rock rising on both sides. After the paved section ends, the last stretch to the reservoir is a gravel track that climbs through switchbacks to around 2,500 metres. Expect washboard, loose stones and dust, and be careful when passing vehicles. It is a route better suited to an adventure bike than a road racer.
The air at this height is thin, dry and cold, and the sun is fierce. Condors are sometimes seen riding the thermals above the ridges, and guanacos and foxes live among the scree. In summer, wildflowers colour the slopes, and the light is very clear. In winter the road closes under snow, and the whole valley is often closed to vehicles from late autumn into spring, so check conditions before you go. Entry to the reservoir area may require a permit or a guided tour, so confirm before planning a visit.
Simple cafés in the lower valley serve empanadas and grilled meat, and weekends bring crowds from the city. Go on a weekday if you can, and aim to be back below the high ground before dark.