The Coloma 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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Coloma’s center stands about 790 ft above sea level. Within three miles the land runs from 710 ft to 2,000 ft, a difference of 1,290 ft: steep hill country. The highest named summit within 15 miles is Sand Mountain, about 4,800 ft, 14 miles east-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 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 6×. 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 5 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 4 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 4 mi of the line.
Schist, gneiss. Age: Paleoproterozoic to Cretaceous, 66 to 2,500 million years old. About 3 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 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.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 smaller units along the line are not listed.
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 Coloma reaches San Francisco Bay and the Pacific Ocean by way of the South Fork American and the Sacramento: about 110 river miles.
Lake on the way: Folsom Lake.
55 miles of the trip are on the Sacramento.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Coloma; river miles along the main stem, rounded.
