The Monticello Dam, which holds back Lake Berryessa, features a morning glory spillway. This type of spillway is basically a giant cement funnel and is also known as The Glory Hole. Rather than spilling over the dam, high waters spill into the funnel. This is the largest in the world, with a diameter of 72 ft (22 m). It is used very rarely, but it is quite the sight to see it being put to use.