The Alta Sierra 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.
Partly cloudy
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Showers likely; cooler
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79° on Nov. 13, 1990, the hottest reading for this week of the year since 1966. Next is 79° in 2008.
Alta Sierra’s center stands about 2,280 ft above sea level. Within three miles the land runs from 1,650 ft to 2,800 ft, a difference of 1,150 ft: steep hill country. The highest named summit within 15 miles is Spaulding Point, about 4,390 ft, 15 miles east-northeast.
Under the town center the state geologic map shows Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains) (mafic-volcanic), from the Jurassic, 145 to 202 million years old.
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 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 17 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 3 mi of the line.
Sandstone. Age: Eocene, 34 to 56 million years old. About 2 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 1 mi of the line.
Schist, gneiss. Age: Paleoproterozoic to Cretaceous, 66 to 2,500 million years old. About 0.6 mi of the line.
Argillite, phyllite. Age: Permian to Jurassic, 145 to 299 million years old. About 0.4 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 Alta Sierra reaches San Francisco Bay and the Pacific Ocean by way of South Wolf Creek, Wolf Creek, the Bear River, the Feather and the Sacramento: about 130 river miles.
75 miles of the trip are on the Sacramento.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Alta Sierra; river miles along the main stem, rounded.
Alta Sierra has a hot-summer Mediterranean climate. Summer afternoons average 88° in July; winter nights fall to about 32° in December. A normal year brings about 9 inches of snow; with the rain, that comes to about 53 inches of water.
On November 14 Alta Sierra normally reaches 60° and falls to 37°. The record high is 78°, in 1974; the record low 25°, in 1985. The most rain on this date, 2.86 in, fell in 1981.
Normals 1991–2020 and records since 1966 at Grass Valley No. 2, 4 miles north, 120 ft higher. NOAA, through RCC-ACIS.
