We dug down into the sand underneath the raised portions and found these beautiful snails. Most of the snails we encountered were ~1-2 cm long.
Purple Olive Snails, Callianax biplicata (formerly Olivella biplicata), are elongate snails with very smooth, polished shells. They're often olive green in color, with purple near the bottom of the shell. But some individuals are very pale and others are dark purple (see below).
Here's a better view of the underside of the shell, highlighting the purple coloration and the shell aperture (opening) that is very long and narrow. Note also the shallow notch at the end of the shell through which the snail can extend a siphon.
Some of the snails were crawling along the surface of the sand. The foot and mantle extend forward and upward like a plow. In the photo below, the foot/mantle are on the left and the short spire at the tip of the shell is on the right.
Purple Olive Snails display predator avoidance strategies when disturbed. They rise up and somersault to move away from potential predators such as sea stars (e.g., Pisaster brevispinus). In the next image you can see a snail in this unusual position with its large foot flared out on the right side. (In this case, the snail was responding to human contact.)
Although sandy beaches can be challenging places for animals to live, this species can be found in intertidal areas on wave-protected sandy beaches along the Pacific Coast from British Columbia to Baja California (and subtidally on wave-exposed coasts).