One of the most wonderful geologic features in the world is the Ausangate Mountain of the Peruvian Andes. The mountain is striped with colors ranging from turquoise to lavender to maroon and gold. However, this "painted mountain" is notoriously difficult to find and get to, requiring several days of hiking to reach its peak deep within the Andes by way of Cusco. The mountain sits at an elevation of 6,384 meters and is located approximately 100 km southeast of the major city Cusco. The local area is rich in geology, from uplifted granitic cliffs to glaciers which have eroded large valleys and the cretaceous limestone "forest" nearby. Rainbow Mountain Peru turned out not to be the beautiful natural wonder that you see on the tourism posters in Cusco.
It was quite the opposite. But we’ve made it back in one piece to now provide a warning to other travelers considering a Rainbow Mountain day tour. Rainbow Mountain is a colorful mountainside in the Andes of Peru. In short, the colors you see were formed by sedimentary mineral layers in the mountain that have been exposed by erosion. The Rainbow Mountain trailhead is located a 3-hour drive from Cusco, where day trips have recently grown quite popular. Rainbow Mountain turned out a true natural wonder, also known as Vinicunca, has become a major touristic attraction. The painted Ausangate Mountain is also considered to be holy and believed to be the deity of Cusco by local Peruvians. It is a site of daily worship and offerings by local citizens.
Every year thousands of Quechua pilgrims visit the Ausangate Mountain for the Star Snow festival which takes place a week before the Corpus Christi feast. The Andes are an incredibly complex mountain chain that extends along the western edge of the South American continent. The subduction of the Nazca plate underneath the South American plate initiated mountain building and uplift of the mountain range. This produced significant volcanism and the introduction of rare and varied mineralogy to the Andes Mountains. The reason we see the rainbow coloration in the stratigraphic layers of the Ausangate Mountain is mainly due to weathering and mineralogy. Red coloration of sedimentary layers often indicates iron oxide rust as a trace mineral. Alike to how a nail will rust and turn red when oxidized, sediments that are iron rich will change when exposed to oxygen and water. This, in combination with uplift and tectonically driven crustal shortening has tilted the sedimentary layers on their side exposing stripped stratigraphic intervals.
The different coloration is due to diverse environmental conditions and mineralogy when the sediment was originally deposited and subsequently diagenetically altered. Moreover, introduction of goethite or oxidized limonite will introduce a brownish coloration to sandstones. Thus, the bright yellow coloration could be due to iron sulphide as trace minerals within the pore cement. Further, chlorite will often color sediments varying shades of green dependent on diagenetic history and concentration. What was simply a calm mountain in the Andes is now inundated with hundreds of tourists who all ascend in droves from Cusco to get their Instagram able shot of the colorful mountain. Though Rainbow Mountain may look good-looking in the photos, we recommend NOT pursuing this hike if it’s been raining and/or until trail improvements are made. It’s not just a strenuous trek. It can be downright dangerous, as evidence by the numerous people witnessed hobbling back to their tourist shuttle.