Plate tectonics is a theory about how the plates are constantly moving on top of a layer of magma that is constantly taking in old crust to recycle it this constant movement causes earthquakes, tsunamis and other geological events. The movement of the Pacific and North American plates cause the old sea floor to be replaced by the now wider North American plate. Also with the movement the continental plate was stretched as the Pacific plate pulled the continental plate to the northwest which again stretched it out. This movement of the plates against each other also created the San Andreas fault which will come up later. What caused the San Andreas fault to be created twenty million years ago was the Pacific plate and the North American plate
