This is a Purple-striped Jelly (Chrysaora purpurata). It's a more southern species and is rare north of San Francisco. I'm not sure if they've been documented at Dillon Beach before?
Here's another view:
Stephanie spotted this jelly in an isolated pool on Sand Point (at the southern end of Dillon Beach). She captured a beautiful photo of the setting this morning:
You might recall that I posted about this species a few years ago — see "Southern drifter?" from 27 July 2014.
For additional information about this handsome jellyfish, visit The Jellies Zone page.
P.S. Many thanks to Stephanie for sharing these wonderful images!
P.P.S. If you see a Purple-striped Jelly, take a photo and send me a message. I'd love to hear about any additional observations.
P.P.P.S. One name for the August full moon (according to the Ojibwe) is the Blueberry Moon. Since the moon is full on August 7th, this seemed like good timing to honor both the jelly — with its dark purple stripes — and the full moon.