The recognition of ethnic and political identities in pre-Conquest Peru has been traditionally based on ceramic styles. In the Central Coast, taking advantage of the existence of historical sources about the Lurin Valley, it has been suggested that coastal ayllus were using preferably Ychsma Style utilitarian pottery, which would also define the culture of the same name; the inhabitants of headwaters of the valley (Huarochirí) would have used so-called «Serrano» Style pottery. The frequency of occurrence of this style in excavated or surveyed sites at Lower Lurin Valley has been interpreted as evidence for highland presence and political importance on the coast. The article tests this hypothesis by analyzing, through Laser Ablation Inducted Couple Plasma Mass Spectrometry (LA-ICP-MS), 600 potsherds from Lower, Middle and Upper Lurin Valley and 116 clay samples from Chillon, Rimac, Lurin and Chilca valleys; the results has been processed by multivariate statistics and spatial analysis (SIG) in order to correlate ensembles of pottery workshops and stylistic groups with areas of clay extraction. The final results show that the Lurin Valley and the Rimac Valley each had its own stylistic and technological tradition in utilitarian pottery; they also show that the hypothetical «Serrano» Style was characteristic of potters in the Lurin Valley, while Ychsma Style was mainly produced in the Rimac Valley. Such findings force us to reinterpret the relationship between highlands and coast during the Late Horizon, including the early Colonial Period, and to subject to criticism the existence of the «Ychsma culture» in the territory of the hypothetical chiefdom of the same name.