Live on the beach at low tide, The back legs are more flexible than the crabs I'm used to, so I had a hard time picking it up to put it back in the water before a dog or seagull made a meal out of it...

23 left valves, 58 right valves.

All found at the edge of the surf on a moderately low tide, in a fairly short strech of beach around the Rio Del Mar Seawall. There were so many, at one point I bent down once to pick up 4! This is very unusual, I typically would find 0-2 of these in that stretch of beach - where it seems most abundant around here. Could that species be experiencing a die off?

22 valve fragments: 19 left, 3 right.

Weird day at the beach yesterday... Afternoon moderately low tide. No shells of any type from Manresa campground to 0.5 mile south of the sea wall. Then pretty significant amount of shells, including many Yoldia Cooperii fragments, and an amazing profusion of Heteroclidus Puctatus

I found this guy at low tide on the beach. I thought it was dead but when I touched it it moved so I carried it up the beach to the vegetation at the base of the dunes. Did not have any fresh water to rinse the sand off - and I thought it probably already had been exposed to more sea water than appropriate,..

2 valve fragments (1 right, 1 left). These might be the smallest sheels I found so far.
BTW, I have lots of observation in need of id confirmation in this taxon: https://www.inaturalist.org/observations/jle152?utf8=✓&q=Yoldia+Cooperii&search_on=&quality_grade=needs_id