While not exactly a "cave" in the common sense, Pluto's Cave (aka Pluto Caves) is a partially collapsed lava tube located about 20 minutes from Edgewood Estates. Lava tubes are created when a molten lava stream cools faster on its surface than its center -- over the course of several days the still-liquid lava inside the tube drains out, leaving the hard crust "tube" which creates the "cave."
There are several of these lava tubes in northern California; Pluto's Cave is located just northeast of Weed off of Highway 97. To get there from the Park, travel north on Hwy 97 to County Road A-12 (approximately 7 miles from Weed), turn left and drive approximately 3 miles until you see a telephone pole on your left with a small sign that says "Pluto's Cave." Turn left on the dirt road and follow it to a parking area at the end of the road. Look for a rock with a white arrow painted on it, and follow the trail marked by the arrow.
Bring flashlights and extra batteries if you intend to explore the caves. There is no fee and they are open year-round.