The early 21st century witnessed a boom in green building in San Francisco and similar cities. Major downtown property owners and investors retrofitted office towers, commissioned green certification, and critically, explored how greening might pay. Greening initiatives transcend corporate social responsibility: they represent a new attempt to enclose and speculate upon "green" value within the second nature of cities. However, this unconventional resource discovery requires a highly partial view of buildings' socio-natural entanglements in and beyond the city. I illuminate these efforts and their obscurities by exploring the experience of an exemplary green building in San Francisco, an office tower that has successively served as a headquarters organizing a vast resource periphery in the American West, a symbol and driver in the transformation of the city's own second nature, a financial "resource" in its own right, and most recently, an asset in an emerging global market for green property.