The Hidden Valley Lake plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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82° on Nov. 12, 2014, the hottest reading for this week of the year since 1954. Next is 81° in 1995.
Hidden Valley Lake’s center stands about 1,170 ft above sea level. Within three miles the land runs from 940 ft to 2,170 ft, a difference of 1,230 ft: steep hill country. The highest named summit within 15 miles is Cobb Mountain, about 4,730 ft, 10 miles west.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 5×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Andesite. Age: Early Pliocene to Pleistocene, 1.5 to 4 million years old. About 8 mi of the line.
Serpentinite. Age: Middle Jurassic to Late Jurassic, 145 to 175 million years old. About 7 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 million years old. About 5 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 2 mi of the line.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 1 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit along the line are not listed.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Hidden Valley Lake reaches San Francisco Bay and the Pacific Ocean by way of Gallagher Creek, Coyote Creek, Putah Creek, South Fork Putah Creek, Prospect Slough, Cache Slough and the Sacramento: about 110 river miles.
Lake on the way: Lake Berryessa.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Hidden Valley Lake; river miles along the main stem, rounded.
Hidden Valley Lake has a hot-summer Mediterranean climate. Summer afternoons average 91° in July; winter nights fall to about 32° in December. About 30 inches of rain fall in a normal year.
On November 14 Hidden Valley Lake normally reaches 64° and falls to 36°. The record high is 81°, in 1995; the record low 23°, in 1978. The most rain on this date, 3.07 in, fell in 1965.
Normals 1991–2020 and records since 1954 at Clearlake 4 SE, 8 miles north, 180 ft higher. NOAA, through RCC-ACIS.
