Check the property discription and see if the mineral rights come with the property. In Texas they do. But I don't know about CA.
Man I live in the middle of the east Texas oil field and I also worked in real estate for years and you will never get mineral rights on land around here. They have been seperated for decades, I would imagine that CA is the same since there is so much oil around southern California.
Standard Oil/Standard of California bought the oil rights up en-mass in the entire Bay Area, if not most of northern California, at least a century ago.
Once in a while, a parcel is found to have been missed, but it is rare. After the Korean War, my oldest brother bought a rare 160 Northern California acres parcel that still had primary water, mineral, and timber rights attached to it.