The hook
When Lake Berryessa fills past the brim, the overflow doesn't run over a dam. It vanishes down a 72-foot hole in the middle of the water.
01Why it's worth it
Monticello Dam holds back Putah Creek to make Lake Berryessa, and instead of an ordinary spillway it uses a "morning glory": a giant concrete funnel standing in the lake just behind the dam. When the water climbs past 440 feet of elevation, it pours over the 72-foot-wide lip and drops nearly 200 feet straight down a shaft that narrows to 28 feet, then turns and runs out into the creek below. Locals call it the Glory Hole. It only performs in wet years, and when it does it pulls a crowd to the rail to watch a whole lake pour into what looks like an open drain with no bottom; in 2017 it ran for the first time in over a decade. In dry years it sits empty, a concrete ring waiting for rain. Under the water it swallows lies the town of Monticello, flooded when the dam went up in the 1950s.
02How to experience it
The spillway is at Monticello Dam on Highway 128 west of Winters, with a small pullout to see it from the rail. The whole point is conditional: it flows only when the lake tops the crest, usually late winter into spring and only in wet years, so check recent lake levels before you make the drive. The rest of the time it's a curiosity rather than a spectacle, worth a look if you're passing but not a trip on its own.