The Thermalito 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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85° on Nov. 11, 1930, the hottest reading for this week of the year since 1906. Next is 85° in 1932.
Thermalito’s center stands about 220 ft above sea level. Within three miles the land runs from 130 ft to 750 ft, a difference of 620 ft: hilly country. The highest named summit within 15 miles is Weiss Hill, about 3,300 ft, 15 miles east.
Under the town center the state geologic map shows Plio-Pleistocene and Pliocene loosely consolidated deposits (sandstone, conglomerate), from the Miocene to Pleistocene, less than 23 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 10×. 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.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 7 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 4 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 2 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 million years old. About 2 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 Thermalito reaches San Francisco Bay and the Pacific Ocean by way of the Feather and the Sacramento: about 140 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 Thermalito; river miles along the main stem, rounded.
Thermalito has a hot-summer Mediterranean climate. Summer afternoons average 95° in July; winter nights fall to about 36° in January. About 27 inches of rain fall in a normal year.
On November 14 Thermalito normally reaches 65° and falls to 40°. The record high is 80°, in 2025; the record low 26°, in 1994. The most rain on this date, 1.37 in, fell in 1953.
Normals 1991–2020 and records since 1906 at Chico University Farm, 18 miles northwest. NOAA, through RCC-ACIS.
