Mission records, however, contain rich demographic and social data essential for understanding the dynamics of culture contact at the regional level (Aschmann 1986:243-244). Analysis of regional dynamics is essential because—to cite one reason—mission documents cannot be used to estimate native population without assessing the extent of conversion. Simply, if large numbers of native peoples remained outside the mission system, then the mission records incompletely reflect the total population. Since the proportion of neophytes to unconverted natives was not a constant, demographic reconstruction based on mission records require analysis of the conversion process. In the balance of this article we analyze data on conversion and demography from the baptismal registers of Mission Nuestra Santisima Senora de El Rosario de Vinadaco, Baja California (Fig. 1).