The processes through which boundaries are made and unmade - conceptually, socially and materially - have been of enduring interest to a wide range of social scientific disciplines including sociology, anthropology, geography, science studies etc. The subject matter of this article - the Yucca Mountain high-level nuclear waste repository in Nye county Nevada, which is meant to keep such waste safe for 10,000 years - constitutes, we contend, a case study of such processes taken to extremes. This in turn makes Yucca Mountain an interesting vantage point from which to (re)view the traditional ontological and epistemological preoccupations characteristic of social science, not so much in terms of abstract theory but rather in terms of concrete practical problems of spatial and temporal organisation.