Fern Cave

Fern Cave opens 1.5 miles south-east of Hospital Rock, near the north-east corner of Lava Beds National Monument in northern California, through a single small hole in the roof. Ferns flourish in the circle of light that falls through it, covering a mound of fallen blocks and soil beneath the opening, and J. D. Howard, who named the cave, noted the toads living among them. Water condensing on the cave walls gives it its unusual environment, and a locked grate across the hole now protects the ferns and the cave's well-preserved pictographs from vandals. A steel staircase leads down onto the mound.

Below lies a big lava tube that can be followed for about 1,300 feet before lava blocks it at both ends. In places it is more than 60 feet wide, with ceilings of 12 to 20 feet upstream, and it may be the downstream continuation of the Bearpaw-Skull system, the great artery that carried lava across this part of the monument, though no one has traced a direct link. At the upstream end, molten lava boiled up into an underground amphitheatre from some deeper tube. Two last flows are frozen on the floor along the cave's whole length, an older one of smooth pahoehoe that drained and left benches along the walls, and a final lobe of spiny lava that ran down the middle, leaving gutters two or three feet deep along its edges.

It is also one of the oldest archaeological sites in the north-western United States, on the National Register since 1975, and sacred to the Modoc. Their oral history tells how the Gwagónus, water spirits, came to the aid of Kemush and went down into the cave to fight the primordial darkness. They sealed it beneath Fern Cave with molten rock at the cost of their water skins and became the first Maklak, the People; the rock gave them their brown skin, and their water skins became the water that still condenses in the cave. Tribal experts read the drawings as a record of the eruption of Mount Mazama, the mountain that is now Crater Lake, when Kemush led the Maklaks underground to shelter while the ash fell. There is no academic consensus on what the pictographs show. During the Modoc War, Kintpuash is said to have used the cave to shelter women and children away from the fighting around the Stronghold.

Because of its fragile ecosystem and its spiritual value to the Modoc, Fern Cave is open only on ranger-led tours by reservation, booked through the park.