Paleontology and geology
The Tertiary was a time of widespread mountain building in Washington and many of the rocks formed during this time are igneous. Marine waters covered the state east of the Cascades during part of this time interval. The sedimentary rocks formed in these waters contain fossils of clams, snails, and crabs, as well as a high diversity of whales and rare marine birds. Coastal swamps were home to a variety of plant and insect life. Fossil leaves, fruit seeds, flowers, and insects occur in great abundance in some of the rocks formed in these swamps. Footprints and rare teeth indicate that small mammals roamed the landscape.