The Blackhawk 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. 17, 1961, the coldest reading for this week of the year since 1903. Next is 25° in 1978.
Blackhawk’s center stands about 960 ft above sea level. Within three miles the land runs from 520 ft to 1,940 ft, a difference of 1,420 ft: steep hill country. The highest named summit within 15 miles is Mount Diablo, about 3,810 ft, 4 miles north.
Under the town center the state geologic map shows Plio-Pleistocene and Pliocene loosely consolidated deposits (sandstone, conglomerate), from the Miocene to Pleistocene, less than 23 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 7×. 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, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 8 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 5 mi of the line.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 3 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 3 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 million years old. About 2 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 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. 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 Blackhawk reaches San Francisco Bay and the Pacific Ocean by way of San Ramon Creek and Walnut Creek: about 25 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Blackhawk; river miles along the main stem, rounded.
Blackhawk has a hot-summer Mediterranean climate. Summer afternoons average 89° in July; winter nights fall to about 39° in January. About 15 inches of rain fall in a normal year.
On November 14 Blackhawk normally reaches 65° and falls to 43°. The record high is 85°, in 1906; the record low 26°, in 1938. The most rain on this date, 1.02 in, fell in 1953.
Normals 1991–2020 and records since 1903 at Livermore, 13 miles southeast, 430 ft lower. NOAA, through RCC-ACIS.
