The hike to the top of Devils Postpile is a bit steep & no railing at the the top. The base (from the lower trail) features iconic columnar basalt rock formations. If you continue, you'll arrive at Rainbow Falls, which has 3 viewpoints. Head down to the base of the falls for an amazing view!
If you do this once the shuttles are running from Mammoth Mountain, you'll want to park at the Mammoth Mountain Inn and took the Reds Meadow Shuttle Bus to the trailhead closest to Devils Postpile. It was a short and easy hike, about 0.5 miles to the base. While many walked past Devils Postpile after a few photos, we took the short but steep trail to the top. The view is worth the extra few minutes. You can loop to the trail with Rainbow Falls or head back down to rejoin the trail you were just on.
Rainbow Falls is about 2.5 miles away on the same trail. A great place for lunch and relaxing and swimming. Surprisingly, there was cell phone reception at the Falls, I was able to call my wife and show her the Falls via Facetime.
Here is a helpful map to show the highlights and stops if you're taking the shuttle.
