The San Gabriel 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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96° on Nov. 13, 1933, the hottest reading for this week of the year since 1877. Next is 94° in 1900.
San Gabriel’s center stands about 400 ft above sea level. Within three miles the land runs from 240 ft to 730 ft, a difference of 490 ft: hilly country. The highest named summit within 15 miles is San Gabriel Peak, about 6,120 ft, 10 miles north.
Under the town center the state geologic map shows Older Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene, less than 2.6 million years old.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 3×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 11 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 7 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 2 mi of the line.
Orthogneiss. Age: Paleoproterozoic to Miocene, 5.3 to 2,500 million years old. About 1 mi of the line.
Quartz-monzonite. Age: Late Triassic, 218 to 218 million years old. About 1 mi of the line.
Granite. Age: Late Triassic, 208 to 208 million years old. About 0.8 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 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 San Gabriel reaches the Pacific Ocean by way of Alhambra Wash, the Rio Hondo and the Los Angeles: about 25 river miles.
Often dry. About 50% 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 San Gabriel; river miles along the main stem, rounded.
San Gabriel has a hot semi-arid climate. Summer afternoons average 84° in August; winter nights fall to about 48° in December. About 14 inches of rain fall in a normal year.
On November 14 San Gabriel normally reaches 73° and falls to 54°. The record high is 93°, in 1933; the record low 36°, in 1880. The most rain on this date, 1.33 in, fell in 1928.
Normals 1991–2020 and records since 1877 from the Los Angeles Downtown Area threaded record (Los Angeles Downtown, 8 miles west-southwest). NOAA, through RCC-ACIS.
