About 150 million years ago, during the late Jurassic period, the area occupied by this national park had a stable climate with abundant moisture.
Dense forests with giant trees grew here, among which were Araucaria mirabilis, an ancient relative of modern species of Araucaria, a kind of evergreen conifer.

This changed at the start of the Cretaceous period, when volcanic eruptions, which coincided with the start of upthrusting of the Andes mountains, buried some of the Patagonian territory in ash and lava.
Part of the forests covered by ash were subjected to the processes of petrification.
This process requires the fallen tree to be in an oxygen-free environment which preserves the original plant structure and general appearance, but which periodically gets inundated by mineral-rich water, replacing the organic structure with silica and other minerals.
The end result is petrified wood.

Some of the fossilised trees were 100 m (328 ft) tall and 3.5 m (11 ft) in diameter.
The site is of particular interest because it shows that the climate of this part of Patagonia was much wetter before the Andes intercepted the humid airflow from the west.
About 150 million years ago, during the late Jurassic period, the area occupied by this national park had a stable climate with abundant moisture. Dense forests with giant trees grew here, among which were Araucaria mirabilis, an ancient relative of modern species of Araucaria, a kind of evergreen conifer.
This changed at the start of the Cretaceous period, when volcanic eruptions, which coincided with the start of upthrusting of the Andes mountains, buried some of the Patagonian territory in ash and lava. Part of the forests covered by ash were subjected to the processes of petrification. This process requires the fallen tree to be in an oxygen-free environment which preserves the original plant structure and general appearance, but which periodically gets inundated by mineral-rich water, replacing the organic structure with silica and other minerals. The end result is petrified wood.
Some of the fossilised trees were 100 m (328 ft) tall and 3.5 m (11 ft) in diameter. The site is of particular interest because it shows that the climate of this part of Patagonia was much wetter before the Andes intercepted the humid airflow from the west.
Bosques Petrificados de Jaramillo National Park