Study of increased metropolitan growth pressure on the Santa Cruz Mountain range, a valuable and relatively undeveloped open space resource in the San Francisco Bay region, led to development of the Early Warning System, a model which can be used by planners for predicting future conflicts between land development and ecological processes. The model maps areas of potential development based on site selection criteria of land-using interests, and then describes the impacts of various types of potential land use on the ecosystem. This approach appears to have substantial flexibility and potential for application to land use planning and control procedures at all levels of government having jurisdiction over non-urbanized lands.