South Dakota has a long-standing history of antagonism between white ranchers and Native Americans. Much of the animosity stemmed from water and grazing rights around the Pine Ridge Reservation. However, the renewed uranium rush in the 1970s brought together Oglala Lakota and their white ranchers and farmer adversaries. The Black Hills Alliance, a coalition of Lakota, ranchers, farmers, and anti-nuclear activists, formed within the context of the nuclear colonial enterprise. Indeed, the nuclear age left a dangerous impression on many Indigenous landscapes and bodies due to resource extraction for uranium on Native lands. This paper explores the nuclear borderland of South Dakota and the politics of uranium mining. Borderlands dynamics are an especially useful lens for viewing the cooperation, cultural exchange, and community-formation that occurred during one of the most remarkable inter-ethnic alliances to combat nuclearism. When white members of the Alliance agreed that the Black Hills needed to be protected from uranium mining, they adopted a newfound recognition of the significance of a mountain range to their cultures and lifestyle. By adopting Indigenous epistemologies of survival and place, the alliance moved beyond short-term environmental issues to long-term mutual cultural understanding.