That's an impressive tangle of "noodles"!
Here's a close-up that might provide some more clues:
If you look closely at the individual strands, you'll see small whitish compartments in a regular pattern. Each of these is a cluster of embryos. There can be 10s to 100s of embryos per cluster (depending on the size of the female laying the eggs)...and up to ~1 million embryos per string!
Here's another view. The animal responsible for these will be revealed below the photo:
And the answer is...these are egg strings of a California Sea Hare (Aplysia californica)!
Stephanie also documented a few adults washing up on the beach:
The embryos will take a little over 1 week to develop. Then the free-swimming larvae (veligers) will spend ~1 month in the plankton before undergoing metamorphosis to become tiny sea hares.
California Sea Hares are uncommon in this region (they're generally a more southern species), so let us know if you spot any and if they're laying eggs.
P.S. Many thanks to Stephanie for sharing these great photos!
P.P.S. For a few other sea hare pictures from Miwok Beach in May 2015, see the post called "Munching at Miwok."