The District owns and manages over 70,000 acres of land in 27 open space preserves, 25 of which are open to the public free of charge, featuring more than 250 miles of trails. The open space preserves are open, 365 days a year, from a half-hour before sunrise until a half-hour after sunset. Open space preserves are generally kept in a natural condition in order to best protect the environment and wildlife habitat and are developed with only the amenities needed to provide low-intensity recreation. In addition to preserve maintenance, the District is involved in resource management, which includes management of both natural and cultural resources. Natural resource management generally consists of protecting, restoring, enhancing, and monitoring native vegetation and wildlife, and monitoring and protecting the quality of geological and hydrological conditions. Cultural resource management consists of identifying and evaluating and protecting archeological sites, key historical structures, and cultural landscapes.