The Jamestown 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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21° on Nov. 12, 1985, the coldest reading for this week of the year since 1903. Next is 24° in 1938.
Jamestown’s center stands about 1,420 ft above sea level. Within three miles the land runs from 1,100 ft to 2,170 ft, a difference of 1,070 ft: steep hill country. The highest named summit within 15 miles is Elizabeth Peak, about 4,920 ft, 12 miles northeast.
Under the town center the state geologic map shows Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (mafic-volcanic, greenstone), from the Paleozoic to Mesozoic, 66 to 542 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.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 5 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 million years old. About 4 mi of the line.
Mafic-volcanic, greenstone. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 4 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 3 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 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 Jamestown reaches San Francisco Bay and the Pacific Ocean by way of Don Pedro Reservoir, 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 Jamestown; river miles along the main stem, rounded.
Jamestown has a hot-summer Mediterranean climate. Summer afternoons average 93° in July; winter nights fall to about 32° in December. About 33 inches of rain fall in a normal year.
On November 14 Jamestown normally reaches 64° and falls to 37°. The record high is 81°, in 1999; the record low 25°, in 1964. The most rain on this date, 2.82 in, fell in 2025.
Normals 1991–2020 and records since 1903 at Sonora, 2 miles east-northeast, 260 ft higher. NOAA, through RCC-ACIS.
