A remnant of an ancient volcanic explosion, Kilbourne Hole was designated a National Natural Landmark in 1975. This crater can be found in a desert basin between the Potrillo Mountains and the Rio Grande in southern Dona Ana County. Kilbourne Hole is roughly elliptical in shape, and is known as a Maar – a pit or depression caused by a volcanic explosion with little material emitted except volcanic gas. The crater is between 24,000 and 100,000 years old, and measures 1.7 miles long by well over a mile across, and is hundreds of feet deep.

Kilbourne Hole has many unique minerals remaining from the eruption. The crusts of the Kilbourne Hole volcanic bombs – objects blown from the volcanic vent in a near plastic state – are dull black or brown, but when broken open they often reveal a brilliant, sparkling yellow and green interior of olivine glass granules.

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