Forged during the Eocene Epoch approximately 50 million years ago, the Chuckanut Formation is composed of layers of sedimentary rock that reveal the area’s former climate and geological environment.
According to the Washington State Department of Natural Resources, the U.S. Exploring Expedition began studying fossil specimens collected from the formation during the mid-19th century. The discovery of coal deposits at Bellingham Bay in 1852 fueled further interest in the formation.
A combination of sandstone, siltstone, sandstone, conglomerate and coal beds makeup the hills and mountains of the Chuckanut Formation. Researchers say the layers of sedimentary rock formed in the vegetated channels and floodplains of winding rivers.
“Abundant leaf fossils found in these rocks show that the climate during that time was warm and humid, resembling that of southeast Asia,” according to the Washington State Department of Natural Resources.
From the Chuckanut Formation, geologists have collected seeds, palm fronds, giant ferns, insects, reptiles, shore birds, large swamp-dwelling mammals, amphibians and shallow aquatic fossils — but fossil extraction isn’t always easy.
“Most Chuckanut fossil sites are in steeply tilted beds that make it difficult to collect large numbers of specimens from a single bed,” according to the Washington State Department of Natural Resources. “Instead, a single exposure may span a stratigraphic range of several meters and contain fossils from several different plant communities.”
More bird, mammal and reptile footprints have been collected from the Chuckanut Formation than animal fossils.
Recently, geologists from Western Washington University discovered a fossilized footprint of a Diatryma, a 7-foot-tall flightless bird. The track was the world’s only-known track of any giant extinct bird and is evidence that the nearly 400-pound bird existed in the Pacific Northwest.
There are many ways you can explore the geology of the Chuckanut Formation. Here are some great spots:
Raptor Ridge Trail
You can start this 8-mile hike at Arroyo Park.
Teddy Bear Cove
Explore more than 1,400 feet of shoreline.
Larrabee State Park
This is a great place to camp in the summer.
Before you go out, make sure to check your local rules for fossil collection. Have fun exploring!
