Population structure analyses and biodistance comparisons forMiddle Moche (550–700 AD), LateMoche (700–850 AD), and Transitional (850–950 AD) period skeletal samples from San José de Moro with a previously reported Middle Moche period sample from Pacatnamú, a nearby Jequetepeque Valley site, and eight samples from Huaca de la Luna and Cerro Oreja, two sites in the Moche Valley, suggest that substantial levels of extralocal gene flow into the Jequetepeque Valley from the adjacent highlands to the east occurred during the demise of the Moche polity there. This process strongly corresponds to evidence for a temporal increase in exotic grave offerings at San José de Moro during the Late Moche and subsequent Transitional periods. The broader implications of these results for our understanding of the demise of the Moche are discussed.