The East Sierra Transect Explanation (not printed on shirt)

This is an idealized picture of the geological relationships from Mt Tom to Deep Springs Valley to 3 km depth. It shows generalized rock units, faults and folds caused by our 600 million year geological history. Insets depict the legend or key to symbols and an extended depth transect to 300 km showing the mantle drip and resulting convection in the mantle.

On the left, or west, Mount Tom is typical of the Sierra Nevada with granites intruding metasediments forming roof pendants of Paleozoic and Mesozoic rocks. The Sierra Nevada Fault zone drops these rocks 1-2 km forming the Owens Valley. Owens Valley is filled with alluvial sediments eroded from the surrounding mountains and volcanic rocks with a long history of eruptions. Deep beneath the surface is a pool of magma, the supply for the Long Valley Caldera and a present intruding mass of magma under Lake Crowley.

The high surface of Owens Valley is dominated by the volcanic rock of the Long Valley Caldera. This former volcano exploded 750,000 years ago, blasting 1200 km3 of rock into a cloud that swept down, burying Bishop area with a thick layer of hot ash, which cooled to form the pink surfaces of the volcanic tableland and cliffs along US 395 on Sherwin Grade. After eruption, the area of Crowley Lake sank along faults, and small volcanoes formed from left over magma, the most notable being Mammoth Mountain. Recent volcanos form a line to the north as the Mono Craters, ending at Mono Lake and Panum Crater (450 years).

East of Owens Valley, the White Mountain fault defines a sharp uplift. This fault has evidence of right-lateral horizontal motion and with similar faults are called the East Sierra Fault Zone.

The White Mountains proper are an uplifted block of sedimentary and igneous rocks 600-80 million years old. They started as a continental shelf, subsequently deformed by several mountain building episodes and intruded by granite bodies. Folds and faults reflect a complex history, with a major regional thrust fault, the Last Chance Thrust, evidence of large horizontal transport. Granite bodies forcefully pushed their way up through mushy metamorphosing sedimentary units, stretching them so they are 1/10 their former thickness.

Deep Springs Valley is a half-graben, sinking like a trap door against a series of normal faults on the east side. A geological playground, the Poleta Folds, are a mapping class area toward the west. Thin, distinct layers are displayed with a series of mappable folds and faults known and feared by thousands of geology students.


The inset on the right is a 300 km deep transect from the central valley to White Mountains. The high velocity drip was formerly beneath the Sierra Nevada, pushing it up. It mechanically delaminated and sank into the mushy mantle, pushing more mush up to buoy up the Sierra Nevada, and spreading out to the east to extend the crust and form the Basin and Range mountains of Death Valley and beyond.

Present earthquake patterns confirm the location of faults on the edges of Owens Valley. Right-lateral movement as well as vertical motion are confirmed by present seismicity. Earthquakes from magma movement also are evident of constant change in our restless earth.

539 words, copyright 2009 terry wright