Lava Beds National Monument

Lava Beds National Monument in Northern California has 150 miles of hiking trails. Skull Cave, shown here, was named for the animal and human skulls discovered there. (Andrew Mariman / For The Times)

Sept. 16, 2014 10:48 AM PT

Late afternoon light hits Schonchin Butte, a cinder cone on the northern flank of Medicine Lake Volcano, the largest in the Cascade Range. The volcano has the greatest concentration of lava tubes in the continental United States. (Andrew Mariman / For The Times)

From left, Brenda and Carron Chernobieff of Bellevue, Wash., Brad Jackson of Tampa, Fla., and Chris Chernobieff, also of Bellevue, explore one of the Fleener Chimneys in the park. The chimneys reach as deep as 50 feet. (Andrew Mariman / For The Times)

Tyler Beaver from Klamath Falls, Ore., visits Sunshine Cave, a relatively easy cave for visitors to negotiate with several vent holes allowing sunlight to filter inside. (Andrew Mariman / For The Times)