<P> The Sierra Nevada adjacent to Lake Tahoe were carved by scouring glaciers during the Ice Ages, which began a million or more years ago, and retreated ~ 15,000 years ago at the end of the Pleistocene . The glaciers carved canyons that are today iconic landmarks such as Emerald Bay, Cascade Lake, and Fallen Leaf Lake, among others . Lake Tahoe itself never held glaciers, but instead water is retained by damming Miocene volcanic deposits . </P> <P> Soils of the basin come primarily from andesitic volcanic rocks and granodiorite, with minor areas of metamorphic rock . Some of the valley bottoms and lower hill slopes are mantled with glacial moraines, or glacial outwash material derived from the parent rock . Sandy soils, rock outcrops and rubble and stony colluvium account for over 70% of the land area in the basin . The basin soils (in the <2 mm fraction) are generally 65--85% sand (0.05--2.0 mm). </P> <P> Given the great depth of Lake Tahoe, and the locations of the normal faults within the deepest portions of the lake, modeling suggests that earthquakes on these faults can trigger tsunamis . Wave heights of these tsunamis are predicted to be on the order of 10 to 33 ft (3 to 10 m) in height, capable of traversing the lake in just a few minutes . A massive collapse of the western edge of the basin that formed McKinney Bay around 50,000 years ago is thought to have generated a tsunami / seiche wave with a height approaching 330 ft (100 m). </P> <P> Lake Tahoe has a dry - summer continental climate (Dsb in the Koeppen climate classification). Mean annual precipitation ranges from over 55 inches (1440 mm) for watersheds on the west side of the basin to about 26 inches (660 mm) near the lake on the east side of the basin . Most of the precipitation falls as snow between November and April, although rainstorms combined with rapid snowmelt account for the largest floods . There is a pronounced annual runoff of snowmelt in late spring and early summer, the timing of which varies from year to year . In some years, summertime monsoon storms from the Great Basin bring intense rainfall, especially to high elevations on the northeast side of the basin . </P>

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