The Claremont 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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23° on Nov. 11, 1950, the coldest reading for this week of the year since 1893. Next is 25° in 1958.
Claremont’s center stands about 1,170 ft above sea level. Within three miles the land runs from 880 ft to 1,820 ft, a difference of 940 ft: steep hill country. The highest named summit within 15 miles is Mount San Antonio, about 10,040 ft, 14 miles north-northeast.
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 6 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 to Holocene, less than 2.6 million years old. About 12 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 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.
Schist, gneiss. Age: Paleoproterozoic to Cretaceous, 66 to 2,500 million years old. About 2 mi of the line.
Gneiss. Age: Paleoproterozoic to Miocene, 5.3 to 2,500 million years old. About 2 mi of the line.
Basalt, andesite. Age: Late Oligocene to Late Miocene, 8 to 25 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 Claremont reaches the Pacific Ocean by way of Chino Creek and the Santa Ana: about 45 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 Claremont; river miles along the main stem, rounded.
Claremont has a hot semi-arid climate. Summer afternoons average 95° in August; winter nights fall to about 43° in December. About 9 inches of rain fall in a normal year.
On November 14 Claremont normally reaches 75° and falls to 48°. The record high is 95°, in 1906; the record low 27°, in 1915. The most rain on this date, 0.54 in, fell in 1972.
Normals 1991–2020 and records since 1893 from the Riverside Area threaded record (Riverside Municipal Airport, 19 miles east-southeast, 320 ft lower). NOAA, through RCC-ACIS.
