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Malapai Hill
Malapai Hill is a small mountain in the middle of Joshua Tree National Park in southeastern California, which may have been part of an ancient volcano. It formed during a period of intrusive activity and either rose above the surface or eventually was exposed by erosion. Its name is a derivative of the Spanish word, ''malpaís''.
==Geography and geology==
The peak rises in Joshua Tree National Park, west of the Hexie Mountains, north of the San Bernardino Mountains and near Queen Valley.〔 Formed by eruptive activity sometime between 8 million and 100,000 years ago, Malapai Hill is the product of the intrusion of magma, into White Tank monzogranite, that cooled as basalt. The exact origin of the landform is not known: it might have been part of an older volcanic complex, or it might have never penetrated the surface but cooled underground and then became exposed as the somewhat softer granite around it was eroded over time.
There are two summits with the true summit rising on the north.〔 The volcanic features include piles of monzogranite and basalt talus on the mountain's steep slopes.
The hill is composed of aphanitic alkaline olivine basalt, with phenocrysts of olivine. Xenoliths of lherzolite are abundant and more rarely of White Tank monzogranite. The lherzolite nodules are interpreted as representing depleted mantle from the area of partial melting that produced the magma.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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