Dodecatheon pulchellum (possibly D. jeffreyi)

Also known as Pretty Shooting Star or Few-Flowered Shooting Star.
Cool thing about this one is that it's backwards. The petals grow away from the center rather than up and around it. This is the one that was growing in a marshy area with no land (though most years it would have been a dry sandbar), so I had to clamber into five inches of water to get the picture.