The Folsom 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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26° on Nov. 17, 1961, the coldest reading for this week of the year since 1856. Next is 27° in 1958.
Folsom’s center stands about 230 ft above sea level. Within three miles the land runs from 120 ft to 500 ft, a difference of 380 ft: rolling country. The highest named summit within 15 miles is Pine Hill, about 2,030 ft, 10 miles east-northeast.
Under the town center the state geologic map shows Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene to Holocene, less than 2.6 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 12×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 10 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 8 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 million years old. About 3 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 3 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 0.3 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Folsom reaches San Francisco Bay and the Pacific Ocean by way of Willow Creek and the Sacramento: about 85 river miles.
55 miles of the trip are on the Sacramento.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Folsom; river miles along the main stem, rounded.
Folsom has a hot-summer Mediterranean climate. Summer afternoons average 93° in July; winter nights fall to about 38° in December. About 18 inches of rain fall in a normal year.
On November 14 Folsom normally reaches 66° and falls to 43°. The record high is 81°, in 2010; the record low 27°, in 1978. The most rain on this date, 0.88 in, fell in 1963.
Normals 1991–2020 and records since 1856 from the Sacramento Area threaded record (Sacramento Airport Asos, 21 miles southwest, 210 ft lower). NOAA, through RCC-ACIS.
