Contemporary urbanization has brought well-documented shifts in the social and economic foundations of U.S. cities through deindustrialization, gentrification, and residential segregation. To these widely recognized shifts, we add historical-environmental changes associated with "relict industrial waste" that accumulates and becomes hidden as cities change over time. This study advances a new analytical framework and data collection strategy for uncovering these relict industrial waste sites and the processes that influence their location, frequency, and conversion. Results affirm that hundreds of potentially hazardous sites exist in older cities and that the vast majority of these sites have converted to other uses, hiding potential relict waste from public, scholarly, and regulatory view. Results also indicate that the types of neighborhood settings in which these sites are found and likelihood of subsequent land-use conversion vary significantly by the city in question. Implications for future research and broader conceptualizations of urbanization are discussed.The social and economic foundations of older U.S. cities have changed dramatically over the past half century through processes of deindustrialization, the emergence of new service economies, rising income inequality, gentrification, and hyper-segregation. These changes are all well known to urban scholars, but missing from these accounts is a well-theorized understanding of the environmental changes wrought, and often then concealed, by these same historic forces. In this study, we address this limitation of prior research by introducing a framework that situates historical-environmental change in relation to the widely recognized social and economic forces that transform cities. At the center of this framework is "relict industrial waste," which refers to hazardous waste that accumulates on industrial sites and remains there, forgotten, when those same sites later convert to more visibly benign land uses, such as offices, restaurants, parks, schools,