The Peruvian south coast between the Tambo and Ilo rivers is a deserted wasteland. Yet tracts of abandoned farmland and expanses of desiccated lomas vegetation indicate that it was once vibrant and productive. Scattered habitations and cemeteries also indicate a pronounced resident Chiribaya population between A.D. 1200 and 1400. While river drainages of the western Andes and their canalized extensions are often treated as primary analytical units of study, our investigation of so-called peripheral intervalley regions points to a highly engineered and intensively managed landscape. When compared to the Ilo Valley, intervalley Chiribaya were organized into smaller communities and managed smaller spring-fed irrigation systems but were also heavily invested in adjacent maritime and lomas resource bases. Utilizing a mixed economic strategy, we argue, these intervalley populations were anything but marginal to the Chiribaya señorío of the Ilo region; rather, they were fully engaged in the social, political, and economic spheres of the late Intermediate period Peruvian south coast and formed a significant component of the Chiribaya cultural landscape. Our results hold implications for other similarly marginalized areas of the Andean coast, where distinct microenvironmental parameters and human ingenuity intersected to significantly transform the western Andes.