Devils Postpile is a wall of columnar basalt up to 60 feet tall in Devils Postpile National Monument, near Mammoth Lakes in the eastern Sierra. The hexagonal columns formed about 82,000 years ago when a deep lava flow cooled slowly and evenly, and a later glacier polished their tops to a tile-like surface.
Details
- Type
- Point of Interest
- Accessibility
- Limited accessibility
Last verified: 6/13/2026
Overview
The postpile is one of the world's better examples of columnar basalt. About 82,000 years ago, lava filling the Middle Fork San Joaquin valley pooled some 400 feet deep. Its uniform composition let it cool very slowly, contracting into the tall, mostly hexagonal columns standing today. A glacier later rode over the formation, shearing and polishing the column tops into a mosaic of smooth tiles.
What to See
A short trail from the ranger station reaches the base of the columns, where a talus pile of fallen sections shows their cross-sections. A spur switchbacks to the top for the glacier-polished surface. The columns read best in mid-morning to midday light.
Getting There
The monument sits in the Reds Meadow valley west of Mammoth Lakes. In summer the access road requires the mandatory Reds Meadow shuttle during operating hours. Snow closes the road and monument much of the year; it typically opens around June through October.