English: Kilbourne Hole is a maar crater and one of Potrillo’s most distinctive features. It was created about 24,000 years ago by the explosive interaction of hot magma and an aquifer. Magma rising from deep within the Earth heated the underground water, producing steam. Pressure built up, culminating in an explosion that blew out an irregularly shaped hole more than a mile across, 1.7 miles long, and hundreds of feet deep. The blast scattered material far and wide and exposed layers of rock that preserved the history of Kilbourne’s bygone water. Among geologists, Kilbourne is also known for its xenoliths—rocks that harbor bits of crust or mantle material. Several kinds of xenoliths are found in and around Kilbourne, especially those containing olivine, the greenish mineral of the gemstone peridot. The presence of olivine can indicate material from the mantle, and olivine-rich rocks were among those brought back from the Moon by the Apollo missions.