Here's why:

* Transform Boundaries: These boundaries are where plates slide horizontally past each other. They are characterized by frequent earthquakes but no volcanic activity.

* Pacific and North American Plates: The San Andreas Fault, a major fault line running through California, is a prime example of a transform boundary. Here, the Pacific Plate is moving northwestward relative to the North American Plate.

It's important to note that while the dominant plate movement is transform, there are also small segments of this boundary where subduction occurs (one plate slides beneath the other). This is the case in the Cascadia Subduction Zone, which is responsible for the volcanic activity in the Cascade Range.