The North San Juan 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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79° on Nov. 13, 1990, the hottest reading for this week of the year since 1966. Next is 79° in 2008.
North San Juan’s center stands about 2,140 ft above sea level. Within three miles the land runs from 1,270 ft to 2,800 ft, a difference of 1,530 ft: steep hill country. The highest named summit within 15 miles is Graveyard Hill, about 4,810 ft, 12 miles northeast.
Under the town center the state geologic map shows Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges) (granodiorite), from the Permian to Tertiary, 2.6 to 260 million years old.
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.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 12 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 5 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 3 mi of the line.
Argillite, phyllite. Age: Permian to Jurassic, 145 to 299 million years old. About 3 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 million years old. About 2 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 million years old. About 0.5 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 North San Juan reaches San Francisco Bay and the Pacific Ocean by way of the Middle Yuba, the Yuba, the Feather and the Sacramento: about 150 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 North San Juan; river miles along the main stem, rounded.
North San Juan has a hot-summer Mediterranean climate. Summer afternoons average 88° in July; winter nights fall to about 32° in December. A normal year brings about 9 inches of snow; with the rain, that comes to about 53 inches of water.
On November 14 North San Juan normally reaches 60° and falls to 37°. The record high is 78°, in 1974; the record low 25°, in 1985. The most rain on this date, 2.86 in, fell in 1981.
Normals 1991–2020 and records since 1966 at Grass Valley No. 2, 12 miles south, 260 ft higher. NOAA, through RCC-ACIS.
