This thesis discusses the post-Middle Horizon archaeology of one of the smaller central coast valleys of Peru. It focuses on a zone between 400 and 1000 metres above sea level and analyses data collected over several field seasons. There are two appendices dealing with ceramic analysi8 and excavations. An introduction defines the problems raised by previous work and discusses field procedures. There is a full treatment of the environment in order to show the potential self-sufficiency of the zone and its importance as a coca-growing area. Over 100 sites are described and dated to one or more periods, from the Early Horizon to the Colonial Period, on the basis of the pottery found in surface collections and excavations. Reasons are given for the shift in 8ettlement location between early and late periods. There follows a treatment of the late architecture, which is divided into three types:- domestic, ritual and community. It is shown that the population lived scattered along the hill slopes or behind the ritual structures located on the alluvial fans of lateral quebradas. The purpose of these ritual structures was to house rites connected with the well-being of ancestor-worshipping groups and as a repository for their dead. Ethnohistorical sources yield further information on the economic, political and social organisation of the valley inhabitants. They confirm relationships between coastal Yungas and highland Yauyos, that the ceramic analysis suggested. During the Late Horizon the Incas established themselves in the upper part of the study area in order to control communications and to enjoy access to coca. The most important changes they made were to build a major road linking the coastal and highland centres of Pachacamac and Jauja and to establish a tambo, whose location is identified in this study. Villages close to the tambo underwent particular Inca influence because they provided the bulk of labour for building and servicing it.