The Jackson 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.
Jackson’s center stands about 1,230 ft above sea level. Within three miles the land runs from 880 ft to 1,760 ft, a difference of 880 ft: hilly country. The highest named summit within 15 miles is Mount Zion, about 2,960 ft, 7 miles east-northeast.
Under the town center the state geologic map shows Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (slate, graywacke), from the Triassic to Late Jurassic, 145 to 252 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 7×. 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 11 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 6 mi of the line.
Sandstone. Age: Eocene, 34 to 56 million years old. About 3 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 3 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 million years old. About 0.7 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 0.5 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 Jackson reaches San Francisco Bay and the Pacific Ocean by way of Jackson Creek, Dry Creek, the Mokelumne, the South Mokelumne, the San Joaquin and New York Slough: about 90 river miles.
Often dry. About 40% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Jackson; river miles along the main stem, rounded.
Jackson 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, 2 miles northwest, 360 ft higher. NOAA, through RCC-ACIS.
