The Ben Lomond 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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89° on Nov. 15, 2008, the hottest reading for this week of the year since 1937. Next is 89° in 2019.
Ben Lomond’s center stands about 360 ft above sea level. Within three miles the land runs from 310 ft to 2,370 ft, a difference of 2,060 ft: mountain country. The highest named summit within 15 miles is Loma Prieta, about 3,780 ft, 13 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 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 6×. 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.
Granodiorite, quartz-monzonite. Age: Early Cretaceous to Late Cretaceous, 66 to 145 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: Eocene to Miocene, 5.3 to 56 million years old. About 2 mi of the line.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 1 mi of the line.
Schist, quartzite. Age: Paleozoic to Mesozoic, 66 to 542 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. 5 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 Ben Lomond reaches the Pacific Ocean by way of the San Lorenzo: about 10 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Ben Lomond; river miles along the main stem, rounded.
Ben Lomond has a warm-summer Mediterranean climate. Summer afternoons average 90° in August; winter nights fall to about 37° in January. About 50 inches of rain fall in a normal year.
On November 14 Ben Lomond normally reaches 72° and falls to 40°. The record high is 88°, in 2021; the record low 27°, in 1985. The most rain on this date, 3.42 in, fell in 1972.
Normals 1991–2020 and records since 1937 at Ben Lomond No. 4, here. NOAA, through RCC-ACIS.
