ALTITUDE: 2 025 masl.


One of the most impressive geological features of the world is the rainbow mountain in the Andes of Peru. The mountain is striped with colors ranging from turquoise to lavender, garnet, and gold. However, this “painted mountain” is notoriously difficult to find and reach and requires several days of walking to reach its highest point deep within the mountains of Cusco region.

The painted mountain of Ausangate is also considered sacred and is believed to be the deity of Cusco by local Peruvians. It is a place of worship and daily offerings of local citizens. Every year, thousands of Quechua pilgrims visit Ausangate Mountain for the Star Snow festival, which takes place a week before the Corpus Christi festival.

The mountain is at an altitude of 6,384 meters and is located approximately 100 km southeast of the main city of Cusco. The local area is rich in geology, from granite cliffs to glaciers that have eroded large valleys and the “forest” of nearby Cretaceous limestone.

The Andes are an incredibly complex mountain range that extends along the western edge of the South American continent. The subduction of the Nazca plate beneath the plate of South America initiated the construction of mountains and the rise of the mountain range. This produced significant volcanism and the introduction of rare and varied mineralogy to the Andes Mountains.

The reason why we see the coloration of the rainbow in the stratigraphic layers of the Ausangate mountain is largely due to weathering and mineralogy. The red coloration of the sedimentary layers often indicates the oxidation of iron oxide as a trace mineral. Similar to the way a nail will oxidize and turn red when oxidized, sediments that are rich in iron will change when exposed to oxygen and water. This, in combination with the remote-controlled and tectonically driven cortical shortening, has inclined the sedimentary layers on its side exposing the stripped stratigraphic intervals.

The different coloration is due to the different environmental conditions and to the mineralogy when the sediment was originally deposited and subsequently diageetically altered. The introduction of oxidized goethite or limonite will introduce a brownish coloration in the sandstones. The bright yellow coloration could be due to the iron sulphide as minerals in the porous cement. In addition, chlorite will often color sediments that vary in shades of green depending on diagenetic history and concentration.

As your eye scans the many layers of the Peruvian painted mountain, you are seeing millions of years of history and all the complexities that are associated there. Understanding the environmental and geological conditions that formed the rocky units we see today is one of the basic components of geology and allows us to better understand our world long before humans walk on this green Earth.