Devil's Postpile was created by volcanic activities before the last Ice Age. The upward movement of lava, upon reaching the earth's surface with its cooling effect, began hardening and shaping into the basalt columns seen now as Devil's Postpile. Such basalt columns, with their very smooth surfaces and columnar shapes, are not uncommon on the West Coast. However, they are quite unique for the Sierra Nevada Mountain Range.

The total distance from the turn-off at State Highway 49 is 24.8 miles, with plenty of opportunities to get lost. Follow this description carefully:

From Camptonville follow State Highway 49 east for 12 miles to the Cal Ida Road, which is on the left, just past the Indian Valley Outpost. Or, from Downieville, drive west on State Highway 49 for 12 miles to the turn off, to the right. As you turn off, note the mileage on your car's odometer for future reference.

Proceed north on Cal Ida Road. The road is narrow and winding, so use caution. Logging traffic can be heavy so you might want to turn on your headlights. After 4.5 miles you will pass the old Cal Ida Mill. Directly after the mill the road forks. Follow the right fork for 11.2 miles. The road is paved and has become Forest Road No. 25. For the next several miles you will be driving through part of the 9,000 acres which burned during the 1987 Indian Fire. The Indian Fire was one of the 1,200 fires which blackened a total of 800,000 California acres during the "Siege of 87".

After traveling 11.2 miles from the old Cal Ida Mill on Road 25 you will pass the Eureka Diggins Area, an historic site from the Gold Rush era when Eureka City was a lively mining town. One mile past Eureka Diggins the pavement ends.

From the end of pavement drive 2.5 miles to a point where the road forks. Take the left fork, staying on Road 25. After 1 mile Road 25 veers to the left. Stay on Road 25. (Do not take Road No. 25-29). After 1.5 miles more the road forks again. Take the left fork, still Road 25. (Do not take Road No. 25-31).

Continue for 1.7 miles to the next fork. This time take the right fork. (Do not take Road No. 25-32 which leads to the Morristown Diggings). Driving the last 0.7 mile, you will reach the trailhead where there is ample parking on the road side.

The trail itself is a very short 150-yard uphill climb to the volcanic rock formation called Devil's Postpile.