The Franks Tract State Recreation Area (Franks Tract) is an example of a complex contemporary park mired in ecological and socio-political contestation of what it is and should be. Located in the Sacramento-San Joaquin Delta, it is a central hub in California’s immense and contentious water infrastructure; an accidental shallow lake on subsided land due to unrepaired levee breaks; a novel ecosystem full of ‘invasive’ species; a world-class bass fishing area; and a water transportation corridor. Franks Tract is an example of an uncommons: a place where multiple realities (or ontologies) exist, negotiate and co-create one another. As a case study, this article focuses on a planning effort to simultaneously improve water quality, recreation and ecology in Franks Tract through a state-led project. The article examines the iterative application of participatory mapping and web-based public surveys within a broader, mixed method co-design process involving state agencies, local residents, regional stakeholders, consultant experts and publics. We focus on what was learned in this process by all involved, and what might be transferable in the methods. We conclude that reciprocal iterative change among stakeholders and designers was demonstrated across the surveys, based on shifts in stakeholder preferences as achieved through iterative revision of design concepts that better addressed a broad range of stakeholder values and concerns. Within this reconciliation, the uncommons was retained, rather than suppressed.