The El Malpais National Monument and El Malpais National Conservation Area are home to a volcanic events dating from 115,000 years ago to as recently as only 2000 years ago! Besides lava flows, cinder cones and great views, they also feature lava tubes. Cavers (and spelunkers) can go into these caves to hike and explore. Here is a sketch of the entrance to one of the lava tubes.
For a larger image and more detail, please click here.