Cinder cones, lava domes, calderas and craters can be found in the area apart from the widest variety of volcanic rocks in all the Southern Zone,[4] for example both primitive basalts and rhyolites.

[8] Most of the stone artifacts found in Pilauco Bajo (dated to c. 12.5 to 13.5 ka BP) are made of dacite, rhyodacite and rhyolite from the Puyehue-Cordón Caulle.

[10] The access through El Caulle is not public as it is not inside Puyehue National Park; and an entrance fee of 10,000 CLP, as of 2009, has to be paid, of which 3,000 are refunded if visitor packs out his garbage.

Puyehue, Cordón del Caulle, and Cordillera Nevada form a northwest trending massif in the Ranco Province of the Andes.

Puyehue is located in the southeast, Cordón Caulle in the center, and Cordillera Nevada, which owes its name to its often snowy appearance from the relatively densely populated Chilean Central Valley, is at the northwestern end.

The main plant species present in these high elevations are Gaultheria mucronata, Empetrum rubrum, Hordeum comosum and Cissus striata.

[13] The volcanic complex that comprises Puyehue, Cordón Caulle and Cordillera Nevada[5] has a long record of active history spanning from 300,000 years ago to the present.

[14] In the past 300,000 years, there have been a series of changes in magmatic composition, locus of volcanic activity, magma output rates and eruptive styles.

This decline was probably due a regional change in the location of the active front of the Southern Volcanic Zone that also affected other volcanoes such as Tronador and Lanín.

It is estimated that some 100,000 years ago in the period between Río Llico and Llanquihue glaciation a large ignimbrite called San Pablo was produced.

During most of this time the volcano was covered by the Patagonian Ice Sheet, leaving glacial striae on many lava outcrops and affecting the volcanic activity.

In Cordillera Nevada this volcanism was expressed from about 117,000 years ago primarily as dacitic lava flows erupted along ring faults.

During the Llanquihue glaciation Puyehue volcano produced some of the most primitive basalts of the Southern Volcanic Zone with a magnesium oxide mass percentage of 14.32, which is in equilibrium with melt from mantle peridotite.

After a failed attempt in 1553, governor García Hurtado de Mendoza founded the city of Osorno in 1558, the only Spanish settlement in the zone, 80 km (50 mi) west of Cordón Caulle.

By the end of the 19th century most of the Central Valley west of Cordón Caulle had been settled by Chileans and European immigrants and an eruption was reported in 1893.

On 13 December 1921, Cordón Caulle began a sub-plinian eruption, with a 6.2 km (4 mi) high plume, periodic explosions and seismicity.

Being located between two sparsely populated and by then isolated Andean valleys, the eruption had few eyewitnesses and received little attention by local media due to the huge damages and losses caused by the main earthquake.

After this explosive phase the eruption changed character to a more effusive one marked by rhyodacitic blocky and Aa type lava flows emitted from the vents along the N135° trending fissure.

A third phase followed with the appearance of short north-north west (N165°) oriented vents transverse to the main fissure which also erupted rhyodacitic lava.

The third phase ended temporarily with viscous lava obstructing the vents, but continued soon with explosive activity restricted to the Gris and El Azufral craters.

In 1994 a temporarily emplaced seismic network registered tremors north of Puyehue's cone which reached IV and V degrees on the Mercalli intensity scale.

By this time, 3,500 people had been evacuated from nearby areas,[22] while an ash cloud reaching 12,000 m (39,370 ft)[23] blew toward the city of Bariloche, Argentina, where the local airport was closed.