Through Bayesian analysis of new radiocarbon dates, this paper demonstrates that the Topará tradition did not emerge until after Paracas monumental sites were ritually closed in the Chincha Valley of the Peruvian south coast. These findings controvert a long-held hypothesis of Topará as a foreign tradition which intruded into the Paracas heartland and initiated the period of transformation known as the Paracas-Nasca transition. We present the first radiocarbon dates from Jahuay, the earliest accepted Topará site. These dates are compared with new analyses of published radiocarbon dates from three other sites associated with this transitional period: a Late Paracas politico-ceremonial site in the Chincha Valley, a Late Paracas settlement in the Palpa Valley in the Río Grande de Nasca Drainage, and an Initial Nasca site in the same valley. This work shows Paracas site closures began earlier than has previously been appreciated and demonstrates that the first appearance of the Topará ceramic style post-dates the onset of Paracas decline in the region’s northern valleys. This analysis represents a successful attempt to develop a radiocarbon-based chronology across a calibration plateau by incorporating stratigraphic data into a Bayesian model.