Scientists were surprised to find a pretty common mineral deep in the San Andreas fault: Talc. If you have used baby powder, you have used talc. The slippery talc contributes to the slipperiness of this section of the San Andrea fault, leading to more frequent and smaller earthquake on this section of the fault.
Talc
Serpentine
A type of rock found along the fault also contributes to its slipperiness: serpentine. Serpentine is a shiny green and black rock that makes the fault weak, which means less force is required for movement. This section of the fault has somewhat regular, moderate earthquakes. Other parts of the San Andreas fault have less frequent, larger earthquakes which might be due to different rocks and minerals in those areas.