The Igo 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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81° on Nov. 12, 2019, the hottest reading for this week of the year since 1960. Next is 80° in 1995.
Igo’s center stands about 1,080 ft above sea level. Within three miles the land runs from 640 ft to 2,030 ft, a difference of 1,390 ft: steep hill country. The highest named summit within 15 miles is Bully Choop Mountain, about 6,910 ft, 12 miles west-northwest.
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 4×. 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 12 mi of the line.
Diorite. Age: Jurassic to Early Cretaceous, 100 to 202 million years old. About 12 mi of the line.
Gneiss, amphibolite. Age: Devonian, 359 to 422 million years old. About 0.6 mi of the line.
Granodiorite, trondhjemite. Age: Early Devonian to Late Devonian, 364 to 400 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 Igo reaches San Francisco Bay and the Pacific Ocean by way of Dry Creek, Cottonwood Creek and the Sacramento: about 290 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Igo; river miles along the main stem, rounded.
Igo has a hot-summer Mediterranean climate. Summer afternoons average 99° in July; winter nights fall to about 39° in January. About 63 inches of rain fall in a normal year.
On November 14 Igo normally reaches 62° and falls to 44°. The record high is 80°, in 1995; the record low 28°, in 1985. The most rain on this date, 3.25 in, fell in 1972.
Normals 1991–2020 and records since 1960 at Whiskeytown Reservoir, 7 miles north, 220 ft higher. NOAA, through RCC-ACIS.
