The exposures of the Chuckanut Formation were once part of a vast river delta; imagine, if you will, the bayou country of the Lower Mississippi.
The siltstones, sandstones, mudstones and conglomerates of the Chuckanut Formation were laid down about 40-54 million years ago during the Eocene epoch, a time of luxuriant plant growth in the subtropical flood plain that covered much of the Pacific Northwest. This ancient wetland provided ideal conditions to preserve the many trees, shrubs & plants that thrived here. Rare bird, reptile and mammal tracks have also been immortalized. Tracks from Diatryma, a large flightless bird, were uncovered in 2009. Diatryma reached up to 9 feet in height, making a living in the grasslands and swamps of the Eocene.