For as much as I love to snowboard, I have never been to Mammoth until a few weeks ago, and it wasn't even for the snow! Being able to experience Mammoth in the summertime was never something that I "needed" to do but I am glad I had the opportunity. I loved it so much I will 100% go back, winter or summer.
After a fun night out in The Village (a center full of restaurants, shops and bars), we spent the entire next day hiking to 2 of Mammoths well known spots: Devil's Postpile National Monument and Rainbow Falls. When I say that it took all day I mean it took 6 hours, so make sure you allow enough time if you plan to visit both spots. You start at the Mammoth Mountain Ski Resort and pay $7.00 per person for a bus ride and entrance into the park. The bus ride is about 30 minutes long and drives through very windy, narrow roads. They cram as many people as they can onto those buses - consider that a warning. Exit stop #6 for Devil's Postpile and it is not too long of a trip to the actual Postpile (less than 2 miles). You can then head to Rainbow Falls from the Postpile but it is about 4 miles. You can even rent horses and horseback ride the trail.
If you can only make one if these sights I recommend Rainbow Falls. It is the most amazing waterfall I have ever seen and you can swim in it!!!! If only I would have know I would have brought my bikini, my floatie and some lunch. Take my advice and plan to chill at the base of the waterfall for a while. The water is freezing, but worth the experience.
We finished our night with an amazing sunset and a crazy firework show to celebrate the USA!