The Colusa 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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22° on Nov. 15, 2020, the coldest reading for this week of the year since 1948. Next is 24° in 1958.
Colusa’s center stands about 70 ft above sea level. Within three miles the land runs from 40 ft to 80 ft, a difference of 40 ft: nearly flat ground. The highest named summit within 15 miles is South Butte, about 2,070 ft, 10 miles east.
Under the town center the state geologic map shows Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene to Holocene, less than 2.6 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 12×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 18 mi of the line.
Rhyolite, dacite, andesite. Age: Pleistocene, 1.5 to 2.5 million years old. About 4 mi of the line.
Rhyolite, dacite, andesite. Age: Pleistocene, 1.5 to 2.5 million years old. About 2 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 million years old. About 0.8 mi of the line.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 0.4 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 Colusa reaches San Francisco Bay and the Pacific Ocean by way of the Colusa Basin Drainage Canal and the Sacramento: about 120 river miles.
85 miles of the trip are on the Sacramento.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Colusa; river miles along the main stem, rounded.
Colusa has a hot-summer Mediterranean climate. Summer afternoons average 92° in July; winter nights fall to about 38° in January. About 17 inches of rain fall in a normal year.
On November 14 Colusa normally reaches 65° and falls to 42°. The record high is 77°, in 2013; the record low 26°, in 2024. The most rain on this date, 1.35 in, fell in 1953.
Normals 1991–2020 and records since 1948 at Colusa 2 SSW, 2 miles south-southwest. NOAA, through RCC-ACIS.
