The Embalse El Yeso sits at 2,500 metres in the cordillera east of Santiago, a glacial reservoir completed in 1964 to regulate the Maipo River and supply water to the capital below. Its turquoise surface — tinted by glacial silt suspended in snowmelt — stretches three kilometres beneath the Andes peaks, visible only after a winding ascent through Cajón del Maipo, a canyon corridor carved by the river over millennia. The reservoir's colour shifts with season and sun angle: milky jade in spring when the thaw peaks, deeper cobalt by late summer. Cajón del Maipo has anchored Santiago's weekend geography since the 1930s, when the first gravel track reached San José de Maipo and opened the cordillera to climbers and engineers. The reservoir itself was built to address chronic water scarcity in the Región Metropolitana, but its setting — framed by the Volcán San José to the south and the glaciated ridge of Cerro El Morado to the east — has made it the most-visited landmark in the canyon. Tour operators began running transport from Santiago in the 1990s, and by the 2020s a full-day Andes excursion to El Yeso had become the city's most-booked mountain trip, drawing visitors who lack the vehicle or route knowledge to drive the 90-kilometre climb themselves. The tour embalse del yeso desde santiago routes follow Ruta G-25 southeast through San José de Maipo, then fork onto the unpaved Ruta G-455, a narrow track that climbs 1,200 vertical metres in 25 kilometres. The road surface deteriorates above the Yeso River junction: washboard ruts, loose scree, and switchbacks that require four-wheel drive or a high-clearance van. Most operators stop at the reservoir's northern shore, where a gravel turnout offers unobstructed views across the water. A handful of excursions continue deeper into the canyon to visit hot springs at Baños Colina or include a picnic stop with alpacas near the Monumento Natural El Morado trailhead. The reservoir itself is a working dam — no swimming or watercraft are permitted, and the access gate closes at 18:00 to prevent vehicles from descending after dark. The canyon's altitude and exposure mean weather shifts rapidly: morning sun can give way to afternoon wind or cloud cover that obscures the peaks within an hour. Operators schedule departures between 07:00 and 08:30 to maximise the early light window, when the reservoir's colour is most saturated and the cordillera remains visible. The round trip typically spans ten to twelve hours, including stops for breakfast in San José de Maipo and a late-afternoon return to Santiago.