Don's Home Places California Dams | Putah Creek Monticello Dam

See Also Wildlife Area near Lake Berryessa

Nestled in the Vaca Mountains forming the border between Napa and Yolo counties, Monticello Dam proudly houses the infamous Glory Hole. The dam, built in 1957 by the Bureau of Reclamation, is a concrete-arch structure with a height of 304 feet and a crest length of 1,023 feet. This dam creates Lake Berryessa, a reservoir spanning 15.5 miles in length and three miles in width when filled to capacity, with an extensive 165 miles of shoreline. It serves multiple purposes, providing irrigation and municipal water supply while also offering flood control.

Lake Berryessa was in the national news in February, 2025 when it reached it's maximum level of 440 feet on February 4th 2025, allowing water to spill over Morning Glory Spillway, aka 'The Glory Hole'. It was stillat 441 fe om March 1st.
It has only reched this level 28 times in its nearly 70-year history. As of Saturday February 15, 2025 following an atmospheric river the water was 3 feet above the spillway still pouring thru the 72 foot diameter spillway narrows down to an 8' wide pipe down to Putah Creek about 100 yards downstream from the dam. The last time it was used prior to that was February 2019.
Click on pictures for an expanded version.
   

They drilled a tunnel to divert Putah Creek around the dam during construction.

When the dam was finished they built the Glory Hole on top of the tunnel entrance.
The opening narrows down to an 28 ft wide tunnel makes a gentle curve to the outlet so things that fall in just go out to putah creek about 700 feet from the opening.
There is a picture of a cormorant going down and the guy who took it went down to see what happened and it had survived and flew off.

Unfortunately in 1997 Emily Schwalek a UC Davis PhD student was killed while swimming there. A good swimmer, witnesses said she was drawn toward the spillway and hung onto the edge for 20 minutes before being sucked down. Rescue efforts were hampered by the current and distance from the shore.

Flow:
The dam has 2 penstocks — structures that control water flow from the bottom of the dam. In the summer the flow rate is 50-60 cubic feet per second.
The maximum full rate of flow 8,500 cubic feet per second. This would happen in anticipation of a heavy rainfall to reduce the level of the lake.

At the lake's peak level, the spillway can drain 48,400 cubic feet per second, which occurs when the lake level rises to 15.5 feet above the Glory Hole.
At 443 height (3ft above the Glory Hole - Feb. 2025 level) - flow is 3,800 cubic feet per second (Enough to fill an olympic sized swimming pool every 23 seconds)

There are minimum flows in the summer as specified in thePutah Creek Riparian Reserve Management Plan for natural resorce preservation and agriculture
In October and November pulses are released to stimulate salmon spawning.
Up to half the water can be diverted from a diversion dam at the end of Lake Solano west of Winters.
The water was up to the deck in the Putah Creek South Fork Preserve in February 2025.

Links:
Putah Creek
The Morning Glory Spillway at Lake Berryessa, aka 'The Glory Hole' | Bartell's Backroads
Flying The Drone Inside of The Glory Hole
How Lake Berryessa's 'Glory Hole' works and how it got its name | The Press Democrat

Northern California's famed 'Glory Hole' spillway is used for first time in years | LA timed Feb 2025 Technically called the Morning Glory spillway, the drainage pipe has been used only 25 times in its nearly 70-year history, according to the Solano County Water Agency | LA Times 2025