Mono Lake is the saline remnant of a much larger lake that filled the the Mono basin during the Pleistocene. The ancient fresh-water lake, Lake Russell, was named for Israel C. Russel, who first mapped the area in 1881. At its highest level, the shore of Lake Russell once lapped against the foot of the Sierra Nevada about 130 m above its current water level. Several lava domes and flows in the middle of the lake were erupted less than about 13,000 years ago. Paoha Island is predominantly a domed mass of lake-bottom sediments that was uplifted by an intrusion of magma beneath the lake as recently as 250 years ago. The lake is 40-50 m deep immediately west of Paoha Island, and several submarine craters have been identified around the island.