At the top of Twin Peaks is located Sutro Tower, the most prominent of San Francisco's radio towers, which can be seen from across the bay. Reservoirs on the hill are owned by the San Francisco Fire Department, and provide free drinking water to most of the city. There is also Christmas Tree Point, a viewing point that offers a clear view of most of San Francisco. Most of the hills are undeveloped, and has been designated at a habitat for many natural resources and endangered species, like the Mission blue butterfly.