The Lake Riverside 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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88° on Nov. 13, 1999, the hottest reading for this week of the year since 1942. Next is 88° in 2016.
Lake Riverside’s center stands about 3,440 ft above sea level. Within three miles the land runs from 2,230 ft to 4,120 ft, a difference of 1,890 ft: steep hill country. The highest named summit within 15 miles is Thomas Mountain, about 6,820 ft, 10 miles 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 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 4×. 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 12 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 4 mi of the line.
Plutonic, gneiss. Age: Paleoproterozoic to Late Cretaceous, 66 to 2,500 million years old. About 3 mi of the line.
Schist, gneiss. Age: Paleoproterozoic to Cretaceous, 66 to 2,500 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 Lake Riverside reaches the Pacific Ocean by way of Cahuilla Creek, Wilson Creek, Temecula Creek and the Santa Margarita: about 50 river miles.
Often dry. About 40% 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 Lake Riverside; river miles along the main stem, rounded.
Lake Riverside has a hot-summer Mediterranean climate. Summer afternoons average 94° in August; winter nights fall to about 29° in December. About 25 inches of rain fall in a normal year.
On November 14 Lake Riverside normally reaches 69° and falls to 34°. The record high is 87°, in 1999; the record low 20°, in 2000. The most rain on this date, 2.39 in, fell in 1946.
Normals 1991–2020 and records since 1942 at Henshaw Dam, 20 miles south, 740 ft lower. NOAA, through RCC-ACIS.
