This paper examines the marine reservoir effect for Tomales Bay, a 25.5-km-long tidal estuary along the northern coast of California. We determined the regional ∆R through radiocarbon (14C) measurements of pre-1950 shells from a museum collection as well as archaeologically recovered shell samples from a historical railroad grade of known construction date. These results are compared against four sets of paired shell and bone samples from two local archaeological sites. Our results indicate little spatial variation along the inner bay, but the proposed ∆R value is lower than those previously reported for nearby areas along the Pacific Coast. We also note potential variability in regional ∆R of approximately 200 14C years for the late Holocene, and comparison with an older paired bone and shell sample points toward more significant temporal variation earlier in time.
