Archaeologists generally have not taken advantage of the distinctive characteristics of assemblages of shellfish remains from prehistoric sites to gain information about movement of people between sites within their territory. I attempt to demonstrate this potential through analysis of shell assemblages obtained through small-scale test excavation at 2 archaeological sites in the interior of Santa Cruz Island: CA-SCRI-796 in the western sector of the island and CA-SCRI-758 at an upland location in the central sector. An aspect of the data analysis focused on strata containing an abundance of red abalone shells, dating sometime between 3700 and 3350 cal BC at CA-SCRI-796 and sometime between 4900 and 4325 cal BC at CA-SCRI-758. Also considered are assemblages from later strata at CA-SCRI-758, dating between 2600 and 1600 cal BC. Alternative hypotheses to account for the differences between the sites in proportions of shellfish taxa represented are the following: differences in proportional abundances of taxa at the localities where site inhabitants collected shellfish, changes over time in the character of shellfish communities, different distances of the sites from sources of shellfish, and variation in the intensity of shellfish collecting. The first alternative appears to account for most of the differences between assemblages, thus providing information about the geographic extent of settlement systems.