The Smelter Knolls consist of several coalescing rhyolite domes and flows with an estimated total erupted volume of 2.2 cubic kilometers. No pyroclastic deposits are exposed, although flow breccias and basal vitrophyres are present. The lava is topaz rhyolite. The two main bodies of the Smelter Knolls are separated by a north-south-trending normal fault, consistent with the orientation of normal faults in Fumarole Butte 15 kilometers to the north. Nearby mafic volcanism dated at 6.1 and 0.3 million years bracket the silicic episode. Smelter Knolls is 24 kilometers west-northwest of Delta, Utah.