The Santa Margarita 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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30° on Nov. 16, 1998, the coldest reading for this week of the year since 1893. Next is 31° in 1982.
Santa Margarita’s center stands about 1,010 ft above sea level. Within three miles the land runs from 940 ft to 2,140 ft, a difference of 1,200 ft: steep hill country. The highest named summit within 15 miles is Black Mountain, about 3,590 ft, 14 miles east.
Under the town center the state geologic map shows Miocene marine rocks (sandstone, mudstone), from the Oligocene to Pliocene, 2.6 to 34 million years old.
The section below crosses 10 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.
Granodiorite, quartz-monzonite. Age: Early Cretaceous to Late Cretaceous, 66 to 145 million years old. About 8 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 5 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 3 mi of the line.
Serpentinite. Age: Middle Jurassic to Late Jurassic, 145 to 175 million years old. About 2 mi of the line.
Siltstone-mudstone. Age: Early Cretaceous, 113 to 145 million years old. About 2 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 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. 4 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 Santa Margarita reaches the Pacific Ocean by way of Yerba Buena Creek, Santa Margarita Creek and the Salinas: about 150 river miles.
Often dry. About 80% 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 Santa Margarita; river miles along the main stem, rounded.
Santa Margarita has a warm-summer Mediterranean climate. Summer afternoons average 80° in August; winter nights fall to about 44° in January. About 22 inches of rain fall in a normal year.
On November 14 Santa Margarita normally reaches 71° and falls to 48°. The record high is 88°, in 2021; the record low 33°, in 1929. The most rain on this date, 2.67 in, fell in 1972.
Normals 1991–2020 and records since 1893 at San Luis Obispo Poly, 7 miles south-southwest, 700 ft lower. NOAA, through RCC-ACIS.
