This paper proposes one possible approach for investigating relationships between the locations of prehistoric sites and of contact-period tribelet territories. First, the general concept of tribelets is discussed, followed by the ethnohistoric record of Costanoan or Ohlone groups on the San Francisco Peninsula. After evaluating available data for prehistoric settlement patterns on the eastern Peninsula, based on 180 reported sites, comparisons are made between clusters of archaeological sites and probable tribelet locations. Subsistence data are summarized for several Late Period sites in the San Francisquito watershed, an area which may have been inhabited by from one to three separate tribelets. Apparent differences in subsistence strategies at these sites are discussed and are used to formulate preliminary hypotheses about relationships between the sites and tribelet areas within the watershed.