The Penngrove 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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91° on Nov. 17, 1932, the hottest reading for this week of the year since 1893. Next is 85° in 1923.
Penngrove’s center stands about 100 ft above sea level. Within three miles the land runs from 30 ft to 590 ft, a difference of 560 ft: hilly country. The highest named summit within 15 miles is Mount Hood, about 2,720 ft, 13 miles north-northeast.
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 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 9×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Dacite. Age: Late Miocene to Late Pliocene, 3 to 7 million years old. About 9 mi of the line.
Sandstone, mudstone. Age: Miocene to Pleistocene, less than 23 million years old. About 6 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 5 mi of the line.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 4 mi of the line.
Andesite, dacite. Age: Middle Miocene to Late Miocene, 9.5 to 13 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 Penngrove reaches San Francisco Bay and the Pacific Ocean by way of Lichau Creek and the Petaluma: about 20 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Penngrove; river miles along the main stem, rounded.
Penngrove has a warm-summer Mediterranean climate. Summer afternoons average 82° in September; winter nights fall to about 38° in December. About 26 inches of rain fall in a normal year.
On November 14 Penngrove normally reaches 66° and falls to 43°. The record high is 83°, in 2010; the record low 20°, in 1916. The most rain on this date, 1.77 in, fell in 1953.
Normals 1991–2020 and records since 1893 at Petaluma Airport, 5 miles southeast. NOAA, through RCC-ACIS.
