Which boundary type is represented by California’s San Andreas Fault?

California’s San Andreas Fault represents a transform boundary between tectonic plates.

At a transform boundary, two plates move mainly sideways past one another. The San Andreas system marks the boundary between the Pacific Plate and the North American Plate. Its motion is predominantly right-lateral strike-slip, meaning the opposite side appears to move to the right when viewed across the fault.

The fault extends for roughly 1,200 kilometers through California. Its movement is not perfectly smooth: sections can lock, allowing stress to build until earthquakes release it. The 1906 San Francisco earthquake was associated with a major rupture along the San Andreas Fault.

Transform boundaries differ from divergent boundaries, where plates move apart and new crust forms, and convergent boundaries, where plates collide. The San Andreas is not primarily a subduction zone, although plate-boundary geometry changes farther north and south.