WESTERN NORTH AMERICA HAS TWO MAJOR PLATE BOUNDARIES
THE
SAN ANDREAS FAULT FORMS THE MOST ACTIVE PART OF THE BROAD BOUNDARY ZONE BETWEEN THE PACIFIC AND NORTH AMERICAN PLATESTHE
CASACADIA SUBDUCTION ZONE IS THE BOUNDARY ALONG WHICH THE SMALL JUAN DE FUCA PLATE SUBDUCTS UNDER THE NORTH AMERICA N PLATE