Uinkaret Volcanic Field

Summary

The field contains at least 213 volcanic cones and associated basaltic lava flows. Studies based upon older dating methods suggest that volcanoes began erupting within the field approximately 3.6 million years ago. The basalt of Mount Trumbull is the oldest unit and erupted atop Mount Trumbull, the highest mountain (2447 m, 8029 ft) in the volcanic field. Many of these early erupted basalts were lavas that flowed over a relatively flat erosional surface. Except for near Mount Emma, very few tephra deposits have been identified, but they may have been removed by erosion. At the end of the initial eruptive period, activity in the region was relatively quiet for approximately 2.6 million years. Around 600,000 years ago prolific eruptive activity occurred for at least 100,000 years, then continued less intensely until about 1,000 years ago. Lava flows originating on the Uinkaret Plateau repeatedly cascaded into the adjacent Grand Canyon to form dams that blocked the Colorado River. These dams have since eroded, but prominent markers such as Vulcan's Throne, a 215-m- (700-ft-) tall cinder cone and source vent for a dramatic lava flow that drapes the Grand Canyon wall, are reminders of these dams. The youngest eruptive unit in the Uinkaret volcanic field is the approximately 1,000-year-old basalt of Little Springs, located about 3 km (2 mi) south of Mount Trumbull and north of Grand Canyon. It originated from two closely associated vents, which coalesced into one large pool of lava that spread both north and south. A red cinder cone associated with the eruption was partially rafted away by the moving lava, and only the southwestern edge of the cone remains. This basalt is comparable in surface characteristics and texture Sunset Crater volcano.