Could be Castilleja affinis ssp. Neglecta
These guys live among the rocks along brackish estuary. Largest have about 4 inch wide carapace.
Seen along gray trail on cattle ranch land in Point Reyes.
Seen at dusk in brackish water. S/he caught a fish and took it over to the bank to eat.
Many shells in muddy banks of brackish estuary at low tide.
Fleshy red stem. Roots in fresh water seep.
Had two explode from out of the grass on separate occasions. Then gone. Like all snipes.
First one that's ever pooped/musked on me. Ew.
on coastal bluff; very low shrub