The Greenhorn 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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3.25 inches of rain fell in two days, the most for this week of the year since records began in 1915. The next wettest, 3.16 inches, fell in 1981.
Greenhorn’s center stands about 4,510 ft above sea level. Within three miles the land runs from 3,930 ft to 6,640 ft, a difference of 2,710 ft: mountain country. The highest named summit within 15 miles is Mount Ingalls, about 8,340 ft, 9 miles northeast.
Under the town center the state geologic map shows Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range) (andesite), from the Late Oligocene to Pleistocene, 2 to 24 million years old.
The section below crosses 4 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.
Andesite. Age: Devonian to Permian, 252 to 422 million years old. About 11 mi of the line.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 million years old. About 7 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 6 mi of the line.
Slate, graywacke. Age: Permian, 252 to 299 million years old. About 0.6 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 Greenhorn reaches San Francisco Bay and the Pacific Ocean by way of Estray Creek, Greenhorn Creek, Spanish Creek, the East Branch North Fork Feather, the North Fork Feather, the Feather and the Sacramento: about 240 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 Greenhorn; river miles along the main stem, rounded.
Greenhorn has a dry-summer warm-summer continental climate. Summer afternoons average 86° in July; winter nights fall to about 19° in January. A normal year brings about 38 inches of snow; with the rain, that comes to about 23 inches of water.
On November 14 Greenhorn normally reaches 53° and falls to 24°. The record high is 74°, in 1929; the record low −1°, in 1915. The most rain on this date, 1.15 in, fell in 1952.
Normals 1991–2020 and records since 1915 at Portola, 17 miles east-southeast, 340 ft higher. NOAA, through RCC-ACIS.
