One can clearly differentiate four geologic formations:

Ischichuca Formation
Most of the visitors can not visit this formation. It has not been explored and analysed so far.

Los Rastros Formation
It is formed by dark coloured rocks that contain coal of vegetable origin. The rocks are greenish and blackish and relatively poor in fossils. Evidently this area had a tropical climate at some time. The Submarine and the Worm are formations of this time. At the bottom of the old lagoon, plants grew but were then slowly covered by sediments so this procedure kept them intact. In the highest part of the Worm there are no ferns, but rather deposits of sand which belong to the time in which the lagoon had already disappeared. The area is covered by small hills and mogotes (small elevations which look like elongated beehives); and vizcachas (Viscacia Viscacia) and guanacos (wild relatives of the llama) dwell here.

Ischigualasto Formation
This formation includes rocks with big hardened layers of volcanic ash. The rock is called Tufa. The colours are much brighter: violet and light brown. They are located in the central area of the valley: Valle Pintado, (Painted Valley). There are algarrobos (carob trees) and brooms here. La Lámpara de Aladino (Aladin's Lamp), El Loro (The Parrot), La Gallina (The Hen) are in Valle Pintado. The fossils of Ischiliguasto come from this formation, the Cinodontes are a good example of them. In this formation fossilised trees have also been found.

Los Colorados Formation
This formation is the youngest in the area. The ravines are 100 to 200 meters high, formed by gritty of red or rosy colour. In this area numerous remains of reptiles have been found. The Riojasaurus Bonapartei (a 9 meters long and 3 meters high reptile), stands out. The inscriptions in the stones are 1200 to 1400 years old and they have been found in the gulches near the harder rocks. These were the rock used to carve arrow tips and scrapers.