Monticello Dam is the dam on Putah Creek, in the Vaca Mountains of Napa County, California, that impounds Lake Berryessa. Construction began in 1953 and was completed in 1958, with the reservoir filling by 1963. The dam is part of the federally administered Solano Project.
Near the dam on the southeast side of the reservoir is a bell-mouth (morning-glory) spillway known as the Glory Hole, which operates only when the reservoir holds excess water. According to SFGate reporting, the spillway flowed in 2017 after heavy rains — its first activation since 2006 — and again in 2019. In 1997 a woman was pulled into and killed by the spillway. The Monticello Dam Powerplant, built in 1983, generates up to 12 MW of hydroelectric power.
The dam and its reservoir are peripheral to the Zodiac case only as the geographic feature that defines the Lake Berryessa crime scene.