Black Rock Desert volcanic field Black Rock Desert volcanic field The Black Rock Desert volcanic field in Millard County, Utah, is a cluster of several volcanic features of the Great Basin such as Pavant Butte and Tabernacle Hill. The field's Ice Springs event was an explosive eruption followed by lava flows that were Utah's most recent volcanic activity (1140–1440 AD). which overlapped the older flows of Pavant Butte. The Pleistocene-Holocene field has been an active tectonic area for approximately 2.7 million years. Within the past 1.5 million years, local volcanism has produced both rhyolitic and basaltic cones from near twenty-four vents from which lava escapes
West Rock Ridge is a dark colored rock, but the iron within it weathers to a rusty brown when exposed to the air, lending the ledges of West Rock Ridge a distinct reddish hue. The rock, which formed 200 million years ago during the late Triassic and early Jurassic periods, frequently breaks into octagonal and pentagonal columns, creating a unique "postpile" appearance. Huge slopes made of fractured rock scree are visible beneath many of the ledges of West Rock Ridge. The ridge is the product of a huge feeder dike that supplied several massive lava flows hundreds of feet deep that welled up