Black Diamond is a city in southeast King County, Washington, set in the Cascade foothills near the upper reaches of the Green River valley, roughly 25 miles southeast of Seattle. The city's name and origins lie in the coal industry: beginning in the 1880s, the Black Diamond Coal Mining Company of California developed the area around its mines, shipping coal to San Francisco and building a company town that gave the city its lasting identity. After the mines closed in the early twentieth century, Black Diamond settled into a long period as a small, quiet town, and the railway depot that once served the mines passed through a series of community uses. Over time the city's location at the edge of the Seattle metropolitan area drew commuters, and it became a residential community for people working in Seattle, Bellevue, and the suburban centers of King County. Today Black Diamond has roughly 7,000 residents. Its character blends a preserved historic core with newer suburban growth, most notably the Ten Trails master-planned community on the city's east side, which brought tree-lined streets, parks, and a new wave of housing built around a village-center concept. Older neighborhoods nearer the original town site retain the scale of the historic mining town. Lake Sawyer, one of King County's larger natural lakes, lies at the city's western edge, and Lake Sawyer Regional Park offers trails, mountain-biking routes, and lake access. State Route 169, the Maple Valley Highway, connects Black Diamond to Maple Valley and Renton, while Highway 18 provides routes toward Interstate 90 and the Puget Sound corridor. The Enumclaw School District serves the city's students.