View of the entrance of Petlog Cave, a rarely visited lava tube in the Medicine Lake Volcano area of Northern California.  This is a main opening w/ several other nearby openings - note the thin roof.  The cave has a couple of initial breakdown openings & this lower-elevated passage goes for about 1,500 feet w/in & contains a well-preserved passage w/ minimal breakdown.  It is part of the same cave system as Harvestmen Cave which is just up the slope.  The unique feature of this cave is a section of shelf that resembles a petrified log.