The Alta 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.
Mostly sunny
Showers likely
Showers likely
Chance of showers
Showers likely; cooler
Showers likely
Partly cloudy
6.06 inches of rain fell in two days, the most for this week of the year since records began in 1893. The next wettest, 5.60 inches, fell in 1950.
Alta’s center stands about 3,630 ft above sea level. Within three miles the land runs from 1,960 ft to 4,590 ft, a difference of 2,630 ft: mountain country. The highest named summit within 15 miles is Black Mountain, about 6,980 ft, 12 miles east-northeast.
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 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.
Argillite, quartzite, phyllite. Age: Ordovician to Triassic, 202 to 487 million years old. About 7 mi of the line.
Andesite. Age: Late Oligocene to Pleistocene, 2 to 24 million years old. About 4 mi of the line.
Mafic-volcanic. Age: Jurassic, 145 to 202 million years old. About 4 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 3 mi of the line.
Mafic-volcanic, greenstone. Age: Paleozoic to Mesozoic, 66 to 542 million years old. About 2 mi of the line.
Peridotite, serpentinite. Age: Neoproterozoic to Early Jurassic, 175 to 1,000 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. 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 Alta reaches San Francisco Bay and the Pacific Ocean by way of Little Bear Creek, the Bear River, the Feather and the Sacramento: about 150 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 Alta; river miles along the main stem, rounded.
Alta has a hot-summer Mediterranean climate. Summer afternoons average 87° in July; winter nights fall to about 34° in December. A normal year brings about 14 inches of snow; with the rain, that comes to about 62 inches of water.
On November 14 Alta normally reaches 58° and falls to 40°. The record high is 83°, in 1933; the record low 18°, in 1916. The most rain on this date, 2.90 in, fell in 1981.
Normals 1991–2020 and records since 1893 at Nevada City, 11 miles west-northwest, 850 ft lower. NOAA, through RCC-ACIS.
