The Acalanes Ridge 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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83° on Nov. 15, 2008, the hottest reading for this week of the year since 1970. Next is 81° in 2010.
Acalanes Ridge’s center stands about 490 ft above sea level. Within three miles the land runs from 70 ft to 1,010 ft, a difference of 940 ft: steep hill country. The highest named summit within 15 miles is Mount Diablo, about 3,810 ft, 9 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 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 13×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 8 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 4 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 2 mi of the line.
Sandstone, mudstone. Age: Paleocene, 56 to 66 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 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. 3 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 Acalanes Ridge reaches San Francisco Bay and the Pacific Ocean by way of Walnut Creek: about 11 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Acalanes Ridge; river miles along the main stem, rounded.
Acalanes Ridge has a warm-summer Mediterranean climate. Summer afternoons average 75° in September; winter nights fall to about 45° in January. About 23 inches of rain fall in a normal year.
On November 14 Acalanes Ridge normally reaches 66° and falls to 50°. The record high is 82°, in 2008; the record low 37°, in 1978. The most rain on this date, 0.82 in, fell in 1972.
Normals 1991–2020 and records since 1970 at Oakland Museum, 13 miles southwest, 460 ft lower. NOAA, through RCC-ACIS.
