Folsom Dam spans the American River about five kilometres north of the city centre and holds back Folsom Lake, a 115-square-kilometre reservoir that serves as the main water supply for the Sacramento region. The dam itself is a large concrete gravity structure completed in 1955 by the US Army Corps of Engineers. Tours of the interior — through the tunnels and inspection galleries inside the dam's massive body — run on selected days and are worth booking ahead.
Even without a tour, the view from the road across the spillway is striking. A visitor centre on the south side of the dam provides context on its construction and flood-control role. The dam has prevented major flooding of Sacramento multiple times, most dramatically in 1986 when the reservoir filled to near capacity during a series of storms. Address: 7794 Folsom Dam Road. Phone: 916/989-7275.