With more than 5,800 acres, this park is the largest natural urban park in the United States. Hiking and biking trails cover the terrain that varies from Cowles Mountain, the highest point in San Diego County, to lakes and streams. The park also encompasses one of the county's most historical sites, Padre Dam, which was California's first aqueduct project built by native Indians for the Franciscan Fathers. In 1995, the Mission Trails Interpretive Center opened for visitors, highlighting the park's resources and describing the history of the area.