The Healdsburg 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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6.04 inches of rain fell in two days, the most for this week of the year since records began in 1893. The next wettest, 5.31 inches, fell in 1920.
Healdsburg’s center stands about 110 ft above sea level. Within three miles the land runs from 60 ft to 820 ft, a difference of 760 ft: hilly country. The highest named summit within 15 miles is Mount Saint Helena, about 4,310 ft, 13 miles east-northeast.
Under the town center the state geologic map shows Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene to Holocene, less than 2.6 million years old.
The section below crosses 10 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.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 7 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 6 mi of the line.
Sandstone, mudstone. Age: Late Cretaceous to Pliocene, 2.6 to 100 million years old. About 4 mi of the line.
Siltstone-mudstone. Age: Early Cretaceous, 113 to 145 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.
Serpentinite. Age: Middle Jurassic to Late Jurassic, 145 to 175 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. 4 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 Healdsburg reaches the Pacific Ocean by way of West Slough and the Russian: about 35 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Healdsburg; river miles along the main stem, rounded.
Healdsburg has a warm-summer Mediterranean climate. Summer afternoons average 89° in July; winter nights fall to about 39° in January. About 43 inches of rain fall in a normal year.
On November 14 Healdsburg normally reaches 65° and falls to 43°. The record high is 86°, in 1905; the record low 27°, in 1916. The most rain on this date, 2.88 in, fell in 1965.
Normals 1991–2020 and records since 1893 at Healdsburg, here. NOAA, through RCC-ACIS.
