<P> Lake Tahoe is fed by 63 tributaries . These drain an area about the same size as the lake and produce half its water, with the balance entering as rain or snow falling directly on it . </P> <P> The Truckee River is the lake's only outlet, flowing northeast through Reno, Nevada, into Pyramid Lake which has no outlet . It accounts for one third of the water that leaves the lake, the rest evaporating from the lake's vast surface . The flow of the Truckee River and the height of the lake are controlled by the Lake Tahoe Dam at the outlet . The natural rim is at 6,223 ft (1,897 m) above sea level, with a spillway at the dam controlling overflow . The maximum legal limit, to which the lake can be allowed to rise in order to store water, is at 6,229.1 ft (1,898.6 m). Around New Year 1996 / 1997 a Pineapple Express atmospheric river melted snow and caused the lake and river to overflow, inundating Reno and surrounding areas . </P> <P> The Lake Tahoe Basin was formed by vertical motion (normal) faulting . Uplifted blocks created the Carson Range on the east and the main Sierra Nevada crest on the west . Down - dropping and block tilting (half - grabens) created the Lake Tahoe Basin in between . This kind of faulting is characteristic of the geology of the adjoining Great Basin to the east . </P> <P> Lake Tahoe is the youngest of several extensional basins of the Walker Lane deformation zone that accommodates nearly 12 mm / yr of dextral shear between the Sierra Nevada - Great Valley Block and North America . </P>

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