The San Francisco 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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4.16 inches of rain fell in two days, the most for this week of the year since records began in 1849. The next wettest, 3.43 inches, fell in 1875.
San Francisco’s center stands about 60 ft above sea level. Within three miles the land runs from 0 ft to 730 ft, a difference of 730 ft: hilly country. Open water lies within three miles. The highest named summit within 15 miles is Mount Tamalpais, about 2,570 ft, 14 miles northwest.
Under the town center the state geologic map shows Quaternary sand deposits, unit 1 (coastal), from the Quaternary, less than 2.6 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 19×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 5 mi of the line.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 4 mi of the line.
Sand. Age: Quaternary, less than 2.6 million years old. About 3 mi of the line.
Serpentinite. Age: Middle Jurassic to Late Jurassic, 145 to 175 million years old. About 0.9 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 0.7 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.
Rain that falls on San Francisco runs straight into San Francisco Bay and the Pacific Ocean.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of San Francisco; river miles along the main stem, rounded.
San Francisco has a warm-summer Mediterranean climate. Summer afternoons average 70° in September; winter nights fall to about 46° in January. About 23 inches of rain fall in a normal year.
On November 14 San Francisco normally reaches 64° and falls to 51°. The record high is 80°, in 2008; the record low 43°, in 1985. The most rain on this date, 1.98 in, fell in 1931.
Normals 1991–2020 and records since 1849 at San Francisco Downtown, here. NOAA, through RCC-ACIS.
