New Poster—Folds and Fossils of the Chuckanut Formation


A new map poster is available titled Folds and Fossils of the Chuckanut Formation in Northwestern Washington. The lidar-derived map enhances views of geologic folds in the Bellingham region of northwestern Washington. With illustrations and text, the poster also describes fossils commonly found in this region.


The steep hills and mountains in and near Bellingham, Washington contain tightly folded siltstones, sandstones, conglomerates, and coal beds of the Chuckanut Formation.

Animation of an aerial photo transitioning to the bare-earth lidar of the map (darker shaded areas are the Chuckanut Formation).

The prominent patterns within the lidar-based map are resistant beds of the formation.  These beds were tilted and folded into a series of mountain-scale, plunging anticlines and synclines due to regional tectonic forces. This deformation, along with faulting (less visible in the lidar) occurred sometime between ~45 and 25 million years ago.

Characteristic tafoni, or
honeycomb weathering, found in the Chuckanut
Formation along the coastline of Larrabee State Park



Fossils found within the Chuckanut Formation record a large, dynamic, and complex ancient (~54 to 45 million year old) river floodplain that teemed with subtropical rain forest life.

Casts of large palm leaf fossils from the Chuckanut Formation on display at Western Washington University in Bellingham.

Abundant leaf fossils found in these rocks show that the climate during that time was warm and humid, resembling that of southeast Asia. Seeds, palm fronds, giant ferns, insects, reptiles (see crocodile footprint on the poster), shore birds, large swamp-dwelling mammals, amphibians, and shallow aquatic fossils have also been collected from these rocks.

Stop by the Washington Geology Library for a free printed copy of the poster or download it here. Check out our Presentation Archive for other cool products!

You can also read more about the Chuckanut Formation here.