The Twain Harte 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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Twain Harte’s center stands about 3,690 ft above sea level. Within three miles the land runs from 2,720 ft to 4,670 ft, a difference of 1,950 ft: steep hill country. The highest named summit within 15 miles is Duckwall Mountain, about 5,800 ft, 8 miles southeast.
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 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.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 15 mi of the line.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 million years old. About 6 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 2 mi of the line.
Limestone, marble. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 1 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 Twain Harte reaches San Francisco Bay and the Pacific Ocean by way of Sullivan Creek, the Tuolumne, the San Joaquin and New York Slough: about 170 river miles.
Lake on the way: Don Pedro Reservoir.
80 miles of the trip are on the San Joaquin.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Twain Harte; river miles along the main stem, rounded.
