The Perris 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. 14, 2021, the hottest reading for this week of the year since 1949. Next is 90° in 1949.
Perris’s center stands about 1,450 ft above sea level. Within three miles the land runs from 1,410 ft to 1,880 ft, a difference of 470 ft: hilly country. The highest named summit within 15 miles is Elsinore Peak, about 3,540 ft, 14 miles south-southwest.
Under the town center the state geologic map shows Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene to Holocene, 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 16×. 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 15 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 6 mi of the line.
Felsic-volcanic, mafic-volcanic. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 3 mi of the line.
Argillite. Age: Paleozoic to Late Jurassic, 145 to 542 million years old. About 0.5 mi of the line.
Plutonic, gneiss. Age: Paleoproterozoic to Late Cretaceous, 66 to 2,500 million years old. About 0.4 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 Perris reaches the Pacific Ocean by way of the San Jacinto, Temescal Wash and the Santa Ana: about 80 river miles.
Often dry. About 60% 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 Perris; river miles along the main stem, rounded.
Perris has a cold semi-arid climate. Summer afternoons average 95° in August; winter nights fall to about 37° in December. About 11 inches of rain fall in a normal year.
On November 14 Perris normally reaches 73° and falls to 41°. The record high is 91°, in 2021; the record low 30°, in 1964. The most rain on this date, 0.62 in, fell in 1953.
Normals 1991–2020 and records since 1949 at March Afb, 8 miles north. NOAA, through RCC-ACIS.
