Last updated: May 29, 2024
Place
Cerro La Jara Stop 7
NPS
Look northward across the road. The broad valley is Valle Grande. A lake filled this valley several times in the past. If the lighting is right, you will be able to see low, flat lying ridges at the base of the mountains in the distance. These ridges are sediments that were deposited on the beaches of a lake.
To the northeast - slightly to your right - you can see Cerro del Medio. Cerro del Medio is the first set of peaks you see rising out of the valley. It is a volcanic dome that was formed a few tens of thousands of years after the caldera collapse, when a large lake partly filled Valle Grande. It was the first volcanic dome to erupt after formation of the caldera. The lava that formed the volcanic dome was very hot and contained a lot of silica. It cooled quickly, possibly because it was erupted underwater, and formed rocks called rhyolite and obsidian.
Obsidian is volcanic glass. When broken, it forms very sharp edges. A skilled toolmaker can make high quality knives and arrow points from obsidian. Beginning more than 10,000 years ago, and for thousands of years, obsidian deposits in Valles Caldera National Preserve were mined and used by people who lived in or visited the area. If you saw small flakes of dark, glassy rock on the Cerro La Jara Trail, they were probably obsidian. Ancestral people used the area to make tools from the obsidian, and the flakes were left behind. Admire them and leave them for the next visitor to see.
Stay where you are for a moment and look around for animals. Then, continue down the trail to your final stop.
To the northeast - slightly to your right - you can see Cerro del Medio. Cerro del Medio is the first set of peaks you see rising out of the valley. It is a volcanic dome that was formed a few tens of thousands of years after the caldera collapse, when a large lake partly filled Valle Grande. It was the first volcanic dome to erupt after formation of the caldera. The lava that formed the volcanic dome was very hot and contained a lot of silica. It cooled quickly, possibly because it was erupted underwater, and formed rocks called rhyolite and obsidian.
Obsidian is volcanic glass. When broken, it forms very sharp edges. A skilled toolmaker can make high quality knives and arrow points from obsidian. Beginning more than 10,000 years ago, and for thousands of years, obsidian deposits in Valles Caldera National Preserve were mined and used by people who lived in or visited the area. If you saw small flakes of dark, glassy rock on the Cerro La Jara Trail, they were probably obsidian. Ancestral people used the area to make tools from the obsidian, and the flakes were left behind. Admire them and leave them for the next visitor to see.
Stay where you are for a moment and look around for animals. Then, continue down the trail to your final stop.