Monticello Dam
Interesting facts
- In February 2017 boaters eager to see the spillway run churned up enough wake to make water spill briefly into the Glory Hole.
- Before the valley was flooded, photographers Dorothea Lange and Pirkle Jones documented the town of Monticello and its people; their pictures were published in 1960.
- The ruins of the drowned town of Monticello reappear when the water level of Lake Berryessa drops low.
- The valley was once part of Rancho Las Putas, an 1843 land grant to José and Sixto Berryessa, after whom the lake is named.
- The arch is about 100 feet thick at its base but only 12 feet thick at the crest.
- Although it lies wholly in Napa County, the dam stands less than 500 feet from the Yolo and Solano county lines.
- The nearby town of Winters opposed the project despite standing to benefit, because of its close ties with Monticello.
- The first concrete was poured in August 1955, and the dam was topped out in November 1957 at a total cost of about 37 million dollars.
- When it first filled in 1963, Lake Berryessa was the second-largest reservoir by volume in California, after Shasta.
- Local pressure kept the Solano Project financed and run separately from the giant Central Valley Project, a choice confirmed by a Senate hearing in 1953.
Why it is worth it
Monticello Dam is best known not for its wall but for a hole in the lake beside it. The dam, a concrete arch 304 feet high and 1,023 feet long across the narrow canyon of Putah Creek in the Vaca Mountains, was built between 1953 and 1957 by the Bureau of Reclamation. Its spillway is a "morning glory" — a bell-shaped concrete funnel 72 feet across at the lip, set in the reservoir a short distance from the dam. When Lake Berryessa rises above the rim, water pours evenly over every side of the circle and vanishes into a shaft that narrows to about 28 feet, reappearing in the canyon below. At full flow it can swallow 48,400 cubic feet per second. It is one of the strangest sights in California water engineering: a perfect round waterfall with no visible bottom.
The lake behind the dam is one of the largest in the state, about 26 miles long and able to hold 1.6 million acre-feet. It covers the Berryessa Valley, once a farming district, and the town of Monticello, settled in the 1840s and home to around 250 people when it was cleared; some 300 graves were moved before the water came. The reservoir first filled in April 1963.
The dam was built for irrigation and water supply rather than power; a small hydroelectric plant of 11.5 megawatts, run by the Solano Irrigation District, was added only in 1983. The Glory Hole spills only after wet winters — it ran most recently in February 2025 — and in dry years the rim stands clear of the water, a concrete ring above a grey void.
Getting there
The dam lies on California State Route 128, which runs right past it; a small parking area next to the dam gives a view of the spillway. Vacaville is about 20 km away and Sacramento about an hour's drive. The nearest airfield is Buchanan Field (CCR) at Concord, about 58 km to the south-west.
On these lists
From the encyclopaedia
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.
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