The Alsea 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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17° on Nov. 16, 2014, the coldest reading for this week of the year since 1936. Next is 19° in 1978.
Alsea’s center stands about 300 ft above sea level. Within three miles the land runs from 260 ft to 1,610 ft, a difference of 1,350 ft: steep hill country. The highest named summit within 15 miles is Marys Peak, about 4,080 ft, 9 miles north-northeast.
Under the town center the state geologic map shows Alluvial deposits (sand, gravel, silt), from the Holocene, less than 12,000 years old.
The section below crosses 4 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.
Sandstone. Age: Middle Eocene, 38 to 48 million years old. About 14 mi of the line.
Basalt. Age: Paleocene to Middle Eocene, 38 to 66 million years old. About 7 mi of the line.
Gabbro. Age: Oligocene, 23 to 34 million years old. About 1 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 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.
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 Alsea reaches the Pacific Ocean by way of the North Fork Alsea and the Alsea: about 50 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Alsea; river miles along the main stem, rounded.
Alsea has a warm-summer Mediterranean climate. Summer afternoons average 83° in August; winter nights fall to about 28° in January. A normal year brings about 5 inches of snow; with the rain, that comes to about 69 inches of water.
On November 14 Alsea normally reaches 53° and falls to 31°. The record high is 69°, in 1999; the record low 20°, in 1978. The most rain on this date, 3.37 in, fell in 1942.
Normals 1991–2020 and records since 1936 at Corvallis Water Bureau, 11 miles northeast, 290 ft higher. NOAA, through RCC-ACIS.
