The Volcano 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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Mostly sunny
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3.95 inches of rain fell in two days, the most for this week of the year since records began in 1943. The next wettest, 2.95 inches, fell in 1950.
Volcano’s center stands about 2,070 ft above sea level. Within three miles the land runs from 1,940 ft to 3,160 ft, a difference of 1,220 ft: steep hill country. The highest named summit within 15 miles is Armstrong Hill, about 5,740 ft, 15 miles east-northeast.
The section below crosses 6 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.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 million years old. About 13 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 7 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 2 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 1 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 1.0 mi of the line.
Limestone, marble. Age: Paleozoic to Mesozoic, 66 to 542 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 Volcano reaches San Francisco Bay and the Pacific Ocean by way of Sutter Creek, Dry Creek, the Mokelumne, the South Mokelumne, the San Joaquin and New York Slough: about 110 river miles.
Often dry. About 30% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Volcano; river miles along the main stem, rounded.
Volcano has a hot-summer Mediterranean climate. Summer afternoons average 93° in July; winter nights fall to about 39° in January. About 32 inches of rain fall in a normal year.
Normals 1991–2020 and records since 1943 at Sutter Hill Cdf, 10 miles west-southwest, 480 ft lower. NOAA, through RCC-ACIS.
