Formed by a series of volcanic eruptions nearly 700,000 years ago, Lookout Mountain is a dominant feature to the north of Mammoth Lakes and east of Hwy. 395. Accessible by graded gravel road in summer and by snowmobile in winter, the summit features a mile-wide crater and provides an excellent 360-degree vantage from which to see the eastern scarp of the Sierra and the various features of the Long Valley Caldera. Historically the dome was an important source of pure obsidian to make spear and arrow points.