The Mokelumne Hill 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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3.95 inches of rain fell in two days, the most for this week of the year since records began in 1943. The next wettest, 2.95 inches, fell in 1950.
Mokelumne Hill’s center stands about 1,480 ft above sea level. Within three miles the land runs from 620 ft to 1,850 ft, a difference of 1,230 ft: steep hill country. The highest named summit within 15 miles is Mount Crossman, about 3,880 ft, 15 miles 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 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 8×. 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 12 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 5 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 2 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 2 mi of the line.
Sandstone. Age: Eocene, 34 to 56 million years old. About 1 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 million years old. About 0.9 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 Mokelumne Hill reaches San Francisco Bay and the Pacific Ocean by way of the Mokelumne, the South Mokelumne, the San Joaquin and New York Slough: about 110 river miles.
Lake on the way: Camanche Reservoir.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Mokelumne Hill; river miles along the main stem, rounded.
Mokelumne Hill has a hot-summer Mediterranean climate. Summer afternoons average 93° in July; winter nights fall to about 39° in January. About 32 inches of rain fall in a normal year.
Normals 1991–2020 and records since 1943 at Sutter Hill Cdf, 7 miles northwest, 110 ft higher. NOAA, through RCC-ACIS.
