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Paoha and Negit Islands, Mono Lake, California

The islands of Mono Lake were built by recent eruptions of lava and cinder and by uplift of the shallow lake bottom caused by the rise of magma beneath the lake. The two islands are less than about 2,000 years old, and the lava flows on the north flank of Paoha Island are only about 250 years old.

Most of Paoha Island consists of layers of lake sediments that were pushed up above the water level by rising magma. The north and east tips of the island consist of craters and lava flows that may have erupted as recently as A.D. 1720-1850.

The lava flows of Negit Island erupted between about 2,000 and 200 years ago. Three separate vents each erupted individual dacite lava flows to form three parallel elongate flows.