It's red snow algae aka "watermelon snow." Usually appears late in the season when snowfields have a lot of water in them. Algae thrives in a liquid not frozen environment. It actually starts off as green looking snow algae. Something about the intensity of light makes the algae turn red to protect itself. It is not that uncommon seeing it if you hike in the Sierras at higher elevations late in spring. I've never eaten it (It is algae after all!) but I've heard people say it does taste like watermelon.