Shell is housing a hermit crab. Link to Blueband Hermit Crab (Pagurus samuelis) obs. https://www.inaturalist.org/observations/100490944

Blue-Ringed Top Snail (Calliostoma ligatum) A.k.a. Blue Topsnail, (formerly called Calliostoma costatum.) Brown striped exterior, nearly cone shaped with several rounded whorls. Worn shells reveal underlying blue color. Grows up to 1" (2.5cm) diameter.

Beachcombers's Guide to Seashore Life of California, J.D. Sept, Rev. ed. 2009, p. 80.