Kilbourne Hole

The rift is characterized by deep sedimentary basins, recent faulting and volcanic activity, and unusually high heat flow upwards from the Earth's mantle.

[8] Kilbourne Hole erupted through alluvium (unconsolidated water-deposited sediments), the Camp Rice Formation and through the pre-existing Afton basalt flow.

The rim cliffs, measuring about 40 feet (12 m) in height, are composed of basalt and exhibit clear columnar jointing (a feature common to many basalt cliffs, including those of Devils Postpile National Monument near Yosemite National Park and Moses Coulee in the Channeled Scablands of Washington), with characteristic reddish-purple, polygonal (mostly hexagonal) columns.

The base of the cliffs is obscured by scree composed of blocks of basalt that have been dislodged from the columns above by the work of erosion and mechanical weathering.

The basalt flow that comprises these columns pinches out (thins) and eventually disappears as it approaches the southwestern rim of the maar.

The ejecta at Kilbourne Hole contains dropstones launched as bombs, usually greater than 2.5 inches across[10] and a large number of xenoliths derived from the lower crust and mantle.

[5] Deep crustal rocks include a variety of granulites of both high-silica (felsic) and low-silica (mafic) compositions, mostly charnockite and anorthosite.

Their characteristics show that they were little altered from their formation 1.6 to 1.8 billion years ago, other than some reheating during the opening of the Rio Grande rift.

Jack Schmitt attended the tests, as well as astronaut Barry Wilmore who was there to assist in simulated moonwalks at the hole.

[13] Kilbourne Hole is located within Organ Mountains–Desert Peaks National Monument and administered by the Bureau of Land Management.