Red Cones Long Valley:
Several small cinder cones are located on the floor and rim of the Long Valley caldera. The youngest cones in the area include the Red Cones 5 km (3.1 miles) south of Mammoth Mountain. Geologists estimate that the Red Cones may have erupted as recently as about 5,000 years ago. During the eruption of both cones lava apparently poured through the breaches and spilled about 1.5 km (0.9 miles) down the east valley wall of the Middle Fork of the San Joaquin River.