![]() ![]() Many volcanic cinder cones can still be seen in the foothills of the Pine Valley Mountains and these have been dated at around 20,000 years old. The contact between the top of the Claron and the bottom of the laccolith can be seen in several locations, most notably near the headwaters of Cottonwood Creek along the southwest corner of the mountain range (see photo below in the gallery), and at the headwaters of Leap Creek north of the Browse Guard Station.Īfter erosion exposed the laccolith, volcanic activity continued and the youngest flows are 1-1.6 million years old. This injected a 3,000 foot-thick layer of monzonite porphyry to form the Pine Valley laccolith. A final surge of magma, unable to find its way to the surface, pushed sideways along the weak seam between the Claron and the overlying volcanic layers. After 4-5,000 feet of volcanic deposited on the Claron Formation, the magma vents were effectively sealed off. ![]() The laccolith was formed during a 20 million-year period of volcanic activity. The Pine Valley Mountains formed from the Pine Valley Laccolith, the largest laccolith in the United States and perhaps the world. The mountains are part of Dixie National Forest and are bordered to the south by the Red Cliffs National Conservation Area. The highest point in the range is Signal Peak at 10,365 feet (3,159 m). The Pine Valley Mountains are a mountain range in Washington County, Utah, United States, spanning the county north of the city of St.
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