A vast park system exists in Santa Clara County, and it was significantly expanded in the late 1970s. The Henry W. Coe State Park, Grant Ranch Park, Sanborn Park, and Vasona Park are a few notable parks. Almaden Quicksilver County Park is another. El Sereno Open Space Preserve is one of the open areas that the county also preserves. In addition, the county is home to the Ulistac Natural Area, an area that is maintained by volunteers. Here, efforts are concentrated on eradicating alien and invasive species while adding native flora to the area, luring migrating birds and butterflies.