Unprecedented urban sprawl, wildfires, erosion, tree die-off, and species decline are some of the sobering realities of anthropogenic planetary disruption today. Tracing the colonial history of the »oasis« as a design principle in landscape architecture, this research project investigates how horticultural and architectural modernism in twentieth-century Southern California continue to shape discourses on postwar environmental crises. Contrasting modes of thought originated in California and converged in the Anthropocene as an interplay of economic and technological forces within a new eco-romanticist human–made nature. This historical study of landscape examines how environmental transformations shaped the rationalization of climate change and natural disasters. Integrating archival research with an analysis of urban and rural development in the region, the project analyzes four typologies of Southern California’s designed landscape—residential garden, city park, urban recreational area, and ecological habitat—against the myth of California as modern architecture’s perfect oasis.