Lava River Cave is a lava tube in northern Arizona's Coconino National Forest. At approximately 0.75-mile long, it is the longest cave of its kind known in Arizona. The cave was discovered by some lumbermen in 1915 and has historically been referred to as "Government Cave" due to its location on the eastern edge of Government Prairie and southeast of Government Peak. Today, Lava River Cave is freely accessible to the general public.
Geologists believe the cave was formed sometime between 650,000 and 700,000 years ago when molten lava erupted from a volcanic vent in nearby Hart Prairie. The top, sides and bottom of the flow cooled and solidified, while lava in the middle flowed out, leaving a hollow space to form the cave. Examples of both ʻAʻā and Pāhoehoe basaltic lava can be seen in the cave.
Wikipedia https://en.wikipedia.org/wiki/Lava_River_Cave_(Arizona)
Address Forest Road 171B, 86001, United States
Coordinates 35°20'31.821" N -111°50'8.328" E