Lava Tube Cave in Mojave Desert National Preserve - same location reported by Death Valley Jim at deathvalleyjim.com/2012/05/04/lava-tube-at-mojave-national-preserve-42712/
which says "In the heart of the Mojave National Preserve there is a large hole in the ground, with a large metal stairwell that leads you beneath the earth’s surface, and into an underground cave. This isn’t your ordinary cave however, this cave was formed many thousands of years ago during a volcanic eruption... Volcanic activity in this area dates back 7.6 million years ago, and the last known lava flow can be traced back 10,000 years. This lava tube was formed when lava flowed across the land, and began to cool on the surface. The lava that was flowing below the surface would continue to flow, and empty out of the tunnel that was created, leaving a lava tube.
The National Park Service installed the stairwell to allow visitors to experience the lava tube from below the surface. There are many small openings that allow sunlight in, thus lighting most of the tube. There are multiple “rooms” within the tube that you can visit, each of them being unique. Give your eyes some time to adjust to the lighting before trying to navigate your way through the tube... The lava tube can easily be reached from Kelbaker Road. From Baker, follow Kelbaker Road for roughly 19 miles. Turn left on Aiken Mine Road, and follow for nearly 5 miles. You will come to a small parking area. From here look for the marked “Lava Tube Trail”. The walk to the lava tube is just a short walk."
ref. file name iPhone-or-D10-Eye-Fi-Apr-26-to-MAy-20-2013-110
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