城市蔓延
Urban sprawl created a backlash in many areas, with local governments limiting growth beyond certain boundaries, reducing lot sizes for building homes, and so on. Open space districts were created in several parts of the state specifically to obtain, manage, and preserve undeveloped land. For example, in the San Francisco Bay Area, the open space districts have created a nearly contiguous range of permanently undeveloped land running through the coastal range and hills surrounding the Bay's urban valleys, enabling the creation of huge natural parks and envisioning a hiking trail that will eventually circumnavigate the Bay in an unbroken loop.