A volcanic fumarole seen in infrared film, Hot Creek, California. Boiling water explodes from a volcanic fumarole in the Long Valley Caldera, near Mammoth. One of many hot springs in the area. This one 'puts the Hot in Hot Springs'. The valley is one of the largest calderas on earth, measuring about 20 miles (32 km) long (east-west) and 11 miles (18 km) wide (north-south).??Long Valley was formed 760,000 years ago when a huge volcanic eruption released very hot ash that later cooled to form