Beginning about 3 million years ago, the Sierra Nevada Fault and the White Mountains Fault systems became active with repeated episodes of slip earthquakes gradually producing the impressive relief of the eastern Sierra Nevada and White Mountain escarpments that bound the northern Owens Valley-Mono Basin region.
Owens Valley is a graben; a down dropped block of land between two vertical faults. Owens Valley is the westernmost graben in the Basin and Range Province. It is also part of a trough which extends from Oregon to Death Valley called the Walker Lane.
The western flank of much of the valley has large moraines coming off the Sierra Nevada. These unsorted piles of rock, boulders, and dust were bulldozed to where they are by glaciers during the last ice age. An excellent example of a moraine is on State Route 168 as it climbs into Buttermilk Country.
This graben was formed by a long series of earthquakes, such as the 1872 Lone Pine earthquake, that have moved the graben down and helped move the Sierra Nevada up. The graben is in fact much larger than the depth of the valley suggests; gravity studies suggest that 10,000 feet (3,048.0 m) of sedimentary rock mostly fills the graben and that a very steep escarpment is buried under the western length of the valley. The topmost part of this escarpment is exposed at Alabama Hills.
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