This hole in a granite boulder is over 500 years old. The ancient Kumeyaay Indians in California / Baja California made these grinding holes, known as "morteros" to grind acorns into flour for food, This site is unregistered, unlisted, I found on a hike in the Japatul Valley area of San Diego County, California. "Japatul", in the Kumeyaay language means "water basket" which describes this valley that contained a small natural reservoir of water.