The Burdell Mountain volcanics are flow-banded porphyritic andesite, volcanic breccia, volcanic mudflow deposits, and minor flow-banded dacite which can be found west of the Petaluma Valley. Dated at about 11 million years old, they are related to the Quien Sabe Volcanics to the southeast and were displaced by the Hayward-Calaveras fault system.
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Burdell Mountain andesite lava flow
The Burdell Mountain volcanics are flow-banded porphyritic andesite, volcanic breccia, volcanic mudflow deposits, and minor flow-banded dacite which can be found west of the Petaluma Valley. Dated at about 11 million years old, they are related to the Quien Sabe Volcanics to the southeast and were displaced by the Hayward-Calaveras fault system.
Quien Sabe Volcanic Field
A view of the southern Quien Sabe Range from high on Basalt Hill in Merced County. The Quien Sabe range is comprised of igneous intrusions, from >9 Ma to >11 Ma, predecessors to the volcanics of the Berkeley Hills and the southeastern equivalent of the Burdell Mountain lavas near Petaluma. Photo courtesy of Stephen W. Edwards
A view of the southern Quien Sabe Range from high on Basalt Hill in Merced County. The Quien Sabe range is comprised of igneous intrusions, from >9 Ma to >11 Ma, predecessors to the volcanics of the Berkeley Hills and the southeastern equivalent of the Burdell Mountain lavas near Petaluma. Photo courtesy of Stephen W. Edwards
Vitrophyre breccia in the Tolay Volcanic Field
This exposure of volcanic breccia is a volcanic rock comprised of broken pieces of vitrophyre, a welded volcanic glass. The breccia is found in the Tolay Volcanics, a sequence of rhyolite, andesite, and basalt at least 1220 m thick. The 9 Ma Tolay Volcanics are equivalent to the Berkeley Hills Volcanics. Photo courtesy of Ross Wagner.
This exposure of volcanic breccia is a volcanic rock comprised of broken pieces of vitrophyre, a welded volcanic glass. The breccia is found in the Tolay Volcanics, a sequence of rhyolite, andesite, and basalt at least 1220 m thick. The 9 Ma Tolay Volcanics are equivalent to the Berkeley Hills Volcanics. Photo courtesy of Ross Wagner.
Subduction zone
A subduction zone is formed where two tectonic plates come together and one plate overrides the other. The plate with lower density, usually comprised of continental crust, stays on top while the denser plate, usually made of oceanic crust, is pushed and pulled beneath, into Earth’s mantle.
A subduction zone is formed where two tectonic plates come together and one plate overrides the other. The plate with lower density, usually comprised of continental crust, stays on top while the denser plate, usually made of oceanic crust, is pushed and pulled beneath, into Earth’s mantle.
Divergent spreading center
A spreading center is formed where two tectonic plates are moving away from each other. Magma from the mantle upwells to fill the space made by the diverging plates, and erupts at the boundary to form new crust.
A spreading center is formed where two tectonic plates are moving away from each other. Magma from the mantle upwells to fill the space made by the diverging plates, and erupts at the boundary to form new crust.
Salton Buttes
The Salton Buttes volcanic field is the youngest and southernmost of the fields associated with the North American and Pacific plate boundary. Five obsidian rhyolite domes erupted on the southern shore of the Salton Sea between 6000 and 500 years ago. The area is active geothermally and seismically, with numerous hot springs and mudpots on the surface.
The Salton Buttes volcanic field is the youngest and southernmost of the fields associated with the North American and Pacific plate boundary. Five obsidian rhyolite domes erupted on the southern shore of the Salton Sea between 6000 and 500 years ago. The area is active geothermally and seismically, with numerous hot springs and mudpots on the surface.