The Charter Oak 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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95° on Nov. 14, 2016, the hottest reading for this week of the year since 1893. Next is 95° in 2021.
Charter Oak’s center stands about 760 ft above sea level. Within three miles the land runs from 530 ft to 1,190 ft, a difference of 660 ft: hilly country. The highest named summit within 15 miles is Iron Mountain, about 7,960 ft, 15 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 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.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 11 mi of the line.
Granodiorite. Age: Permian to Tertiary, 2.6 to 260 million years old. About 7 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 3 mi of the line.
Orthogneiss. Age: Paleoproterozoic to Miocene, 5.3 to 2,500 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 1 mi of the line.
Basalt, andesite. Age: Late Oligocene to Late Miocene, 8 to 25 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.
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 Charter Oak reaches the Pacific Ocean by way of Walnut Creek and the San Gabriel: about 30 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 Charter Oak; river miles along the main stem, rounded.
Charter Oak has a hot-summer Mediterranean climate. Summer afternoons average 91° in August; winter nights fall to about 45° in December. About 20 inches of rain fall in a normal year.
On November 14 Charter Oak normally reaches 75° and falls to 50°. The record high is 95°, in 2016; the record low 29°, in 1916. The most rain on this date, 1.30 in, fell in 1928.
Normals 1991–2020 and records since 1893 at Pasadena, 17 miles west, 100 ft higher. NOAA, through RCC-ACIS.
