Quebrada de Humahuaca

The hills are made of many layers of rock. Each layer has its own color.

Some rocks are very, very old.

Geologist Luís Vítor Duarte writes that the colors of the valley come from many layers of rock, made over more than 600 million years. Some layers formed in the sea and some were laid down by rivers. Different minerals in the rocks give them different colors.

Faults and folds have tilted and stacked the layers. Erosion today wears away the softer rocks faster than the harder ones, which makes the stripes stand out.

Duarte (Revista de Ciência Elementar, 2025) describes rock units spanning more than 600 million years: metasedimentary rocks (quartzites, schists) and sedimentary rocks (conglomerates, sandstones, mudstones) with some carbonates, laid down as marine and river settings alternated. Their mineral composition gives the different colors.

The record (late Proterozoic, Cambrian, Ordovician, Cretaceous, Cenozoic) is discontinuous and structurally complex, cut by faults and folds in a compressive zone. Present-day erosion is selective, removing less resistant rock faster, which brings out hills such as the Cerro de los Siete Colores.

One famous hill is called the Hill of Seven Colors. A small town sits at its foot.

Another is called the Painter's Palette.

Visit Argentina says the village of Purmamarca sits at the foot of the Cerro de los Siete Colores, the Hill of Seven Colors, with reds, oranges and browns in the earth. A trail called the Camino de los Colorados goes around it for 3 kilometers, a walk of about an hour.

At Maimará, more than 2,300 meters above sea level, the Paleta del Pintor, or Painter's Palette, shows yellows, ochers, violets and reds in a zigzag.

Duarte explains the Cerro de los Siete Colores at Purmamarca as colored rocks stacked over one another along faults and angular unconformities. The Paleta del Pintor at Maimará is a succession of tilted latest-Cretaceous layers, cut by gullies that give the illusion of folds.

There the Yacoraite Formation, a mix of carbonate and siliciclastic deposits, is known internationally for its stromatolites; it also holds footprints of some of the last dinosaurs, because it includes the Cretaceous-Paleogene boundary. Visit Argentina says the Hornocal range, at 4,761 meters and called the hill of 14 colors, is visited from Humahuaca.

People have walked and traded along this valley for a very long time.

Farmers still use old stone fields here.

UNESCO says people have used the valley as a major trade route for the past 10,000 years, carrying people and ideas between the high Andes and the plains. Along it are the remains of many old settlements, from early hunters and farmers to the time of the Inca Empire.

At Coctaca there are stone-walled terrace fields that UNESCO says are thought to be about 1,500 years old, and are still farmed today. Tilcara, Purmamarca, Maimará and Humahuaca are towns in the valley; Humahuaca is the largest.

UNESCO lists successive settlements along the route: hunter-gatherer and early farming communities (9000 BC to AD 400), large structured farming societies (AD 400-900), pre-Hispanic towns and villages (900-1430/80) and the Inca Empire (1430/80-1535), followed by Spanish-era towns. Stone-walled terrace fields at Coctaca, thought to have begun about 1,500 years ago, are still in use.

Duarte notes that archaeological records at the Pucará of Tilcara point to people living there since at least the 8th century AD. UNESCO adds that today's population keeps its traditions in the landscape.

Cacti called cardones grow in this dry valley. Llamas live here too.

In the photo, green trees grow beside the riverbed.

Geologist Luís Vítor Duarte writes that cacti called cardones are typical of this valley, and that you may meet llamas, members of the camel family, at any moment. Beside the Pucará of Tilcara, Visit Argentina says, a high-altitude botanical garden shows plants of the region: cacti, cardones, and medicinal and fragrant plants.

In the photo, green trees and fields line the wide riverbed, while the dry slopes above are mostly bare.

Cardones (cacti) characterize the valley, and llamas, Andean camelids, can be met at any time (Duarte 2025). Visit Argentina describes the Jardín Botánico de Altura beside the Pucará of Tilcara, which displays plants typical of the region: cacti, cardones and medicinal and aromatic plants.

UNESCO places the valley between the high Puna plateau and eastern wooded areas, and notes that many of its old field systems are still in use as part of a continuing agricultural system.

The sun is strong here. Wear a hat and sunscreen.

The valley is high up, so go slowly.

Visit Argentina suggests walking the Camino de los Colorados early in the morning or later in the afternoon, to avoid the strong midday sun. The CDC suggests a hat with a brim all the way around, sunglasses and sunscreen.

Some places nearby are very high, like the Hornocal at 4,761 meters. The CDC says children can get altitude sickness just like adults; going up slowly helps the body adjust, and a headache is the main sign.

Sun: Visit Argentina advises the Camino de los Colorados in the early morning or later afternoon to avoid intense midday sun; CDC sun safety recommends a wide-brimmed hat, UV-blocking sunglasses, protective clothing and broad-spectrum sunscreen.

Altitude: the CDC Yellow Book says children are as susceptible to acute mountain sickness as adults, that headache is its cardinal symptom, and that ascending gradually gives the body time to acclimatize.