Pahvant Butte, Dormant volcano in Millard County, United States

Pahvant Butte is a tuff cone in the Sevier Desert with a north peak at 5,751 ft and a south peak at 5,486 ft, roughly 1,000 ft above the valley floor. The cone is about 1.5 mi across at its base and has a breach on its southwestern side. A raised beach formed by waves of Lake Bonneville surrounds much of its lower rock.

Pahvant Butte erupted about 15,500 years ago from the floor of Lake Bonneville, then roughly 85 m deep. The phreatomagmatic blast threw steam, ash and basaltic fragments into the air, spawning large waves and building a tuff cone. Between 1140 and 1440 AD, lava flows from the Ice Springs eruption overlapped its base.

Locals call the butte "Sugarloaf Mountain". On the southeast rim of the inner depression stand a concrete building and two rings of concrete obelisks, begun in 1923 by A. H. Hood to generate wind power and never finished.

Access is via Route 257 from Highway 6/50, followed by a drive on a maintained dirt road to reach the site. Bring a vehicle with good ground clearance since road conditions can be rough and dusty.

The site features the Lace Curtain, a rock face displaying delicate white patterns formed by mineral deposits in volcanic tuff. These intricate structures developed over thousands of years as groundwater slowly filtered through and crystallized minerals.