On our recent trip, we approached the park from the north, and the first sight we beheld was beautiful Reflection Lake. In the morning light it was serene and quiet, and it was strange to consider the violence that led to the lake's formation (along with nearby Manzanita Lake). The forest hides the hummocky surface of the landscape that surrounds the lake, but a short distance up the road, the origin of the lake becomes clear.
An aerial shot of the Lassen vicinity shows the Chaos Crags in sharp outline. They are the barren snow-free peaks to the left of the main cone of Lassen Peak (the Crags lie north of Lassen; the picture is oriented towards the southeast). Given the dense thick forest that surrounds the volcanoes and the barren nature of the Crags, they have to be exceedingly young, and dating indeed places their age at about 1,100 years before the present. Six individual domes were erupted during a period of about 60 years.
The Chaos Crags are excellent examples of plug domes, short steep cones produced by highly viscous lava flows. The lava emerged like toothpaste from the ground, and as it cooled, the surface of the lava contracted, breaking up and forming huge debris piles on the margins of the cone.
The six domes have been creatively named A, B, C, D, E, and F. Domes E and F can be seen in the picture below, while Dome D dominates the bottom picture.
In any other setting, the Chaos Crags would be the central focus of a volcanic park, but the much taller peak of Lassen stands less than two miles away, so they tend to be somewhat ignored. That's too bad because there are few better examples of plug domes to be found anywhere, and the youthfulness of the Jumbles suggests continuing geologic activity. A stop among the chaos of the Crags and Jumbles is a great introduction to the geology of Lassen Volcanic National Park!