Lava Beds National Monument

Over 1,100 lava tubes crisscross the lands of far northeastern California, arcing between the cinder cones that stretch from the eastern slopes of Mt Shasta to the border with Nevada
These lava tubes actually do not tend to form large mazes or deep underground chambers, and only several are large enough to comfortably walk through. The National Monument protects many of these and has developed a handful by putting in metal staircases, allowing us to avoid having to abseil down jagged pumice precipices.
This particular cave, known as Skull Cave, is notable for its sheer size and depth, caused by three convergent lava tubes creating a chamber and passageway roughly three times the diameter of the average lava tubes in the area.
As we sit at over 6,000 ft elevation on a high, cold, and mostly barren plateau, permanent ice fills the bottoms of some of these deeper caves. This ice had never melted for thousands of years. Bubbles of ancient gas and rocks frozen in time lie suspended in the ice.
However, it is now melting at increasing rates, risking collapses of floor structures, openings into deeper lava tubes, and releasing ancient material from its suspension.