Monticello Dam is a 304-foot (93 m) high concrete arch dam in Napa County, California, United States constructed between 1953 and 1957. The dam impounded Putah Creek to create Lake Berryessa in the Vaca Mountains.
Lake Berryessa is currently the seventh largest man-made lake in California. Water from the reservoir primarily supplies agriculture in the Sacramento Valley downstream. The dam is noted for its classic, uncontrolled morning-glory-type spillway. The diameter at the lip is 72 ft (22 m). Locally, the spillway is also known as the “Glory Hole”. [source]