Answer: The mineral that underlies the San Andreas Fault near Parkfield is talc.
Step-by-step explanation:
The fault zone near Parkfield, California is located near a large deposit of talc. Talc is a mineral composed of magnesium silicate, and is commonly found in the Earth's crust. The San Andreas Fault, which is one of the most active fault lines in North America, crosses this talc deposit and plays a role in the tectonic activities in the region, and in particular, the earthquake activity in the Parkfield area.