Florissant Fossil Beds National Monument - Volcanoes / Lava Flows

Aerial view of ancient volcanic mudflows Linda Lutz-Ryan Volcanoes can be a source of both destruction and creation. In the case of Florissant Fossil Beds, volcanoes that existed 34 - 35 million years ago led to the creation of delicate impression and compression fossils of leaves and insects and also the permineralization of redwood trees into some of the largest diameter petrified tree stumps in the world.

This ancient volcanic system, sometimes referred to as the Guffey Volcanic complex, was a large composite volcano with multiple vents. A series of broad, muddy lahars or volcanic mudflows initially buried parts of an ancient mixed hardwood forest, encasing the bottom 15 feet of large redwood trees in siliceous mud. Later in time, another mudflow impounded a stream creating a large 12 mile long lake called Ancient Lake Florissant.

Subsequent ash falls from the ancient volcano blanketed the land and fell directly into the lake. Weathered ash turned to clay at the bottom of the lake making an excellent matrix for preserving leaves and insects.

Leaves and insects that died and fell to the bottom of the lake were buried quickly by more weathered ash and preserved as delicate compression and impression fossils.