The Sonora 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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21° on Nov. 12, 1985, the coldest reading for this week of the year since 1903. Next is 24° in 1938.
Sonora’s center stands about 1,840 ft above sea level. Within three miles the land runs from 1,460 ft to 3,170 ft, a difference of 1,710 ft: steep hill country. The highest named summit within 15 miles is Duckwall Mountain, about 5,800 ft, 14 miles east.
Under the town center the state geologic map shows Paleozoic marine rocks, undivided, unit 4 (Western Sierra Nevada) (argillite, quartzite, phyllite), from the Ordovician to Triassic, 202 to 487 million years old.
The section below crosses 8 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.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 11 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 million years old. About 3 mi of the line.
Mafic-volcanic, greenstone. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 3 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 3 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 2 mi of the line.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 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. 2 smaller units 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 Sonora reaches San Francisco Bay and the Pacific Ocean by way of Don Pedro Reservoir, the Tuolumne, the San Joaquin and New York Slough: about 170 river miles.
Lake on the way: Don Pedro Reservoir.
80 miles of the trip are on the San Joaquin.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Sonora; river miles along the main stem, rounded.
Sonora has a hot-summer Mediterranean climate. Summer afternoons average 93° in July; winter nights fall to about 32° in December. About 33 inches of rain fall in a normal year.
On November 14 Sonora normally reaches 64° and falls to 37°. The record high is 81°, in 1999; the record low 25°, in 1964. The most rain on this date, 2.82 in, fell in 2025.
Normals 1991–2020 and records since 1903 at Sonora, here, 160 ft lower. NOAA, through RCC-ACIS.
