The Little Grass Valley 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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Little Grass Valley’s center stands about 5,200 ft above sea level. Within three miles the land runs from 4,510 ft to 6,050 ft, a difference of 1,540 ft: steep hill country. The highest named summit within 15 miles is Mount Fillmore, about 7,680 ft, 7 miles east.
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 9 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: Late Oligocene to Pleistocene, 2 to 24 million years old. About 8 mi of the line.
Mafic-volcanic, greenstone. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 5 mi of the line.
Mafic-volcanic. Age: Permian to Jurassic, 145 to 299 million years old. About 3 mi of the line.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 million years old. About 3 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 2 mi of the line.
Phyllite. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 0.8 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 3 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 Little Grass Valley reaches San Francisco Bay and the Pacific Ocean by way of the South Fork Feather, the Feather and the Sacramento: about 190 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 Little Grass Valley; river miles along the main stem, rounded.
