The McDermitt Caldera is a large, oval-shaped caldera west of McDermitt in southeastern Oregon and northern Nevada in the United States. It is about 28 miles (45 km) wide north to south and 22 miles (35 km) wide east to west. The western part of the caldera is in the Trout Creek Mountains, and the northern part is in the Oregon Canyon Mountains.The caldera was formed when a lava dome made of ryholite collapsed about 16 million years ago.