Answer:
Skamania County is located on the North American Plate, just like the rest of the state of Washington. The plate immediately to the front is the Juan de Fuca Plate, which runs alongside the coast of Washington.
In fact, most of the United States is located on the North American tectonic plate, including Alaska. Only Western California is located on another plate: The Pacific Plate, whose boundary with the North American Plate is the famous San Andreas Fault.
