The Mount Cayley volcanic field formed as a result of the ongoing subduction of the Juan de Fuca Plate under the North American Plate at the Cascadia subduction zone along the British Columbia Coast. This is a long fault zone running off the Pacific Northwest from Northern California to southwestern British Columbia. The plates move at a relative rate of over per year at an oblique angle to the subduction zone. Because of the very large fault area, the Cascadia subduction zone can produce large earthquakes of magnitude 7.0 or greater. The interface between the Juan de Fuca and North American plates remains locked for periods of roughly 500 years. During these periods, stress builds up on the interface between the plates and causes uplift of the North American margin. When the plate finally slips, the 500 years of stored energy are released in a massive earthquake.