Sometimes, when two plates meet, they don’t collide. If the plates are moving in the same direction, they will slide alongside each other.
Don’t be fooled by the easy sound of the word slide, however. Whenever plates meet, there is great stress on the surface of Earth. When two plate edges meet and slide along each other, earthquakes occur. Rocks at the plate edges (called faults) may be pulverized into powder.
Such is the case along the San Andreas Fault in California, where some of the actual edges of the fault can be seen. Here, massive solid granite rocks are pressed together with the force of thousands of tons.
Just about the only thing left after the plates meet is fine rock powder—and earthquakes.