The Potrero 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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91° on Nov. 11, 2025, the hottest reading for this week of the year since 1948. Next is 90° in 1999.
Potrero’s center stands about 2,340 ft above sea level. Within three miles the land runs from 1,690 ft to 3,040 ft, a difference of 1,350 ft: steep hill country. The highest named summit within 15 miles is Long Valley Peak, about 4,820 ft, 14 miles north-northeast.
Under the town center the state geologic map shows Mesozoic granitic rocks, unit 2 (Peninsular Ranges) (tonalite), from the Middle Jurassic to Late Cretaceous, 66 to 175 million years old.
The section below crosses 2 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.
Tonalite. Age: Middle Jurassic to Late Cretaceous, 66 to 175 million years old. About 16 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 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.
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 Potrero reaches the Pacific Ocean by way of Potrero Creek, Cottonwood Creek and the Tijuana: about 40 river miles.
Often dry. About 30% 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 Potrero; river miles along the main stem, rounded.
Potrero has a hot-summer Mediterranean climate. Summer afternoons average 95° in August; winter nights fall to about 33° in December. About 16 inches of rain fall in a normal year.
On November 14 Potrero normally reaches 72° and falls to 37°. The record high is 85°, in 2016; the record low 21°, in 2000. The most rain on this date, 0.47 in, fell in 1952.
Normals 1991–2020 and records since 1948 at Campo, 8 miles east, 290 ft higher. NOAA, through RCC-ACIS.
