The Owyhee Mountains were forced up by the Owyhee Batholith 40 million years ago. Some geologists believe that Owyhee Granite is part of the Idaho Batholith, isolated from the main batholith by the passage of the Yellowstone hotspot. Much of the range's granite is covered by Miocene rhyolite that erupted as a result of a meteorite impact 17 million years ago. The range is surrounded by the younger volcanic rocks of the Snake River Plain, and is still covered in places by extensive deposits of older sedimentary rock. Where Owyhee granite has been exposed to the surface, it has formed impressive outcroppings and an occasional dome.