California Code, Fish and Game Code - FGC § 8341

All of the species of clams commonly known as littlenecks, chiones and hard-shell cockles, including thin-shelled littleneck, common littleneck, Japanese littleneck, rough-sided littleneck, smooth chione, wavy chione, and banded chione, may be taken at any time, except in the waters of Marin County, where they may be taken only between September 1st and March 31st.

No such clams measuring less than one and one-half inches in greatest diameter may be taken, possessed, transported, or sold.

The bag limit on such clams is 50 per day, in the aggregate.  Not more than one daily bag limit of such clams may be possessed by any person during one day.

Clams of the species herein designated, when legally taken outside the State and brought within the State pursuant to this code, may be possessed, transported, and sold without restrictions, except that all shipments of such clams into this State shall be accompanied by a bill of lading, or invoice, showing the species, total number or weight, and the origin of the clams.