The Oso 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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6.36 inches of rain fell in two days, the most for this week of the year since records began in 1911. The next wettest, 5.56 inches, fell in 2001.
Oso’s center stands about 190 ft above sea level. Within three miles the land runs from 140 ft to 3,350 ft, a difference of 3,210 ft: mountain country. The highest named summit within 15 miles is Three Fingers, about 6,670 ft, 13 miles east-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 4×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 8 mi of the line.
Silt, sand. Age: Holocene, less than 12,000 years old. About 6 mi of the line.
Arkose. Age: Late Cretaceous to Eocene, 34 to 100 million years old. About 4 mi of the line.
Graywacke, argillite, siltstone. Age: Jurassic to Late Cretaceous, 66 to 202 million years old. About 2 mi of the line.
Metasedimentary. Age: Devonian to Permian, 273 to 422 million years old. About 2 mi of the line.
Schist. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 2 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 Oso reaches the Pacific Ocean by way of the North Fork Stillaguamish, the Stillaguamish and the West Pass: about 40 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Oso; river miles along the main stem, rounded.
Oso has a warm-summer Mediterranean climate. Summer afternoons average 79° in August; winter nights fall to about 30° in January. About 83 inches of rain fall in a normal year.
On November 14 Oso normally reaches 46° and falls to 35°. The record high is 67°, in 1934; the record low −3°, in 1955. The most rain on this date, 2.90 in, fell in 1991.
Normals 1991–2020 and records since 1911 at Darrington Ranger Station, 15 miles east, 360 ft higher. NOAA, through RCC-ACIS.
