The ground here was a fortress before it was a park. In 1872 and 1873 Kintpuash, known to the army as Captain Jack, held this lava country with about sixty Modoc men against a force that grew past a thousand soldiers, and held it for five months. It was the only major Indian war fought in California. The reason it lasted that long is underfoot: the lava is broken into trenches, collapses and tubes that shelter a defender and expose anyone crossing open ground.
The rock came from the Medicine Lake shield volcano over the last half million years. Lava moving downhill crusts over on top while the inside keeps running, and when the flow drains away it leaves the tube behind. Lava Beds National Monument holds more than 800 of them.
Some of those tubes hold ice all year. Cold air is heavier than warm air, so it settles into a tube that dips and it does not flush out in summer. Water seeping through the roof freezes on the floor and stays frozen, which is how you get a permanent ice floor under a desert in northern California.
More than twenty five caves are open for self guided visits, and Mushpot Cave by the visitor centre is lit and interpreted, which makes it the sensible first one. Some caves, including Fern Cave and Crystal Ice Cave, are ranger led and need a reservation.
Take a hard hat, gloves and two lights per person. The Park Service also screens for white nose syndrome, so gear worn in other caves may be refused. Ask at the visitor centre before going underground rather than after.
Other places on the map within a couple of hours.
