Kingston Canyon is one of the deepest antecedent canyons in the High Plateaus subprovince of the Colorado Plateaus. Here the E Fork of the Sevier River flows westward transversely across the gently E tilted Sevier Plateau, which is developed on a basin-range fault block uplifted more than 1500m along the Sevier fault zone on the W. Upper Tertiary rhyolites, uncommon in SW Utah, occur both on the northern rim and in the bottom of Kingston Canyon. Those on the northern rim consist of lava flows and volcanic domes of the rhyolite of Forshea Mountain, dated by K/Ar methods at 7.6Ma old. Those in the bottom of Kingston Canyon, the rhyolite of Phonolite Hill, are especially well exposed and provide spectacular examples of a pyroclastic cone whose base is about at river level and a steep-sided volcanic dome emplaced into and through these deposits. The pyroclastic deposits, formerly 500 or more metres thick, consist of airfall, mudflow, and ash-flow(?) material of rhyolite and foreign lithic fragments especially olivine basalt. The dome consists of flow-banded, mostly devitrified rhyolite as much as 500m thick; it has been dated by K/Ar methods at 5.4Ma. In addition to the rhyolites, a dome and lava-flow complex, the rhyodacite of Dry Lake, occurs near the northern rim and is considered to postdate the rhyolite of Forshea Mountain and predate the rhyolite of Phonolite Hill. -from Authors
Additional Publication Details
Origin and structural implications of upper Miocene rhyolites in Kingston Canyon, Piute County, Utah.