The San Geronimo 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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6.85 inches of rain fell in two days, the most for this week of the year since records began in 1902. The next wettest, 6.57 inches, fell in 1942.
San Geronimo’s center stands about 840 ft above sea level. Within three miles the land runs from 290 ft to 1,540 ft, a difference of 1,250 ft: steep hill country. The highest named summit within 15 miles is Mount Tamalpais, about 2,570 ft, 7 miles south-southeast.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 12×. 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: Jurassic to Cretaceous, 66 to 202 million years old. About 6 mi of the line.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 5 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 4 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 2 mi of the line.
Mica-schist. Age: Early Cretaceous, 110 to 143 million years old. About 1 mi of the line.
Siltstone-mudstone. Age: Early Cretaceous, 113 to 145 million years old. About 0.7 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 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 San Geronimo reaches the Pacific Ocean by way of San Geronimo Creek and Lagunitas Creek: about 16 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of San Geronimo; river miles along the main stem, rounded.
San Geronimo has a warm-summer Mediterranean climate. Summer afternoons average 83° in July; winter nights fall to about 42° in January. About 44 inches of rain fall in a normal year.
On November 14 San Geronimo normally reaches 64° and falls to 46°. The record high is 81°, in 2010; the record low 25°, in 1916. The most rain on this date, 3.10 in, fell in 1952.
Normals 1991–2020 and records since 1902 at Kentfield, 7 miles east-southeast, 700 ft lower. NOAA, through RCC-ACIS.
