Plural of batholith; massive underground bodies of cooled magma that are typically several miles across and form the cores of mountain ranges.
Greek bathos 'depth' + lithos 'stone', pluralized in English with -s. The concept emerged from 19th-century geological studies of mountain formation.
The Sierra Nevada mountains in California are built on a gigantic batholith that covers thousands of square miles—it's so large that the entire range is essentially sitting on a foundation of cooled underground magma!
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