The Arroyo Grande 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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25° on Nov. 17, 1958, the coldest reading for this week of the year since 1906. Next is 26° in 1938.
Arroyo Grande’s center stands about 120 ft above sea level. Within three miles the land runs from 10 ft to 550 ft, a difference of 540 ft: hilly country. The highest named summit within 15 miles is Hi Mountain, about 3,170 ft, 14 miles northeast.
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 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 8×. 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: Oligocene to Pliocene, 2.6 to 34 million years old. About 7 mi of the line.
Sand. Age: Quaternary, less than 2.6 million years old. About 4 mi of the line.
Sandstone, mudstone. Age: Miocene to Pleistocene, less than 23 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 1 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 1 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.
Arroyo Grande has a warm-summer Mediterranean climate. Summer afternoons average 75° in September; winter nights fall to about 40° in December. About 13 inches of rain fall in a normal year.
On November 14 Arroyo Grande normally reaches 70° and falls to 45°. The record high is 91°, in 2008; the record low 30°, in 1985. The most rain on this date, 1.66 in, fell in 1953.
Normals 1991–2020 and records since 1906 from the Santa Maria Area threaded record (Santa Maria Public Airport, 17 miles south-southeast, 120 ft higher). NOAA, through RCC-ACIS.
