The Sonoma 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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84° on Nov. 15, 2005, the hottest reading for this week of the year since 1893. Next is 82° in 1906.
Sonoma’s center stands about 80 ft above sea level. Within three miles the land runs from 20 ft to 1,090 ft, a difference of 1,070 ft: steep hill country. The highest named summit within 15 miles is Mount Hood, about 2,720 ft, 13 miles north-northwest.
Under the town center the state geologic map shows Older Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene, less than 2.6 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 8×. 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 10 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 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.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 0.6 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 Sonoma reaches San Francisco Bay and the Pacific Ocean by way of Nathanson Creek, Steamboat Slough, Second Napa Slough and Sonoma Creek: about 16 river miles.
Often dry. About 50% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Sonoma; river miles along the main stem, rounded.
Sonoma has a warm-summer Mediterranean climate. Summer afternoons average 86° in July; winter nights fall to about 38° in January. About 28 inches of rain fall in a normal year.
On November 14 Sonoma normally reaches 66° and falls to 42°. The record high is 82°, in 2010; the record low 22°, in 1985. The most rain on this date, 2.05 in, fell in 1953.
Normals 1991–2020 and records since 1893 at Sonoma, here. NOAA, through RCC-ACIS.
