It is an easy 0.5 mile hike to the base of Devils Postpile National Monument (only open during summer months). It is a fantastic display of columnar basalt that was created by lava flowing and then cooling into mostly hexagonal shaped columns. From the base, there is a short but quite steep hike to the top of the rock formation which looks like hexagonal tiles.
From the Postpile, you can continue on the trail for about another 2 miles to get to Rainbow Falls which is a stunning 100 ft waterfall. Return on the same trail.