The Knappa 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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5.39 inches of rain fell in two days, the most for this week of the year since records began in 1887. The next wettest, 5.30 inches, fell in 2015.
Knappa’s center stands about 30 ft above sea level. Within three miles the land runs from 0 ft to 850 ft, a difference of 850 ft: hilly country. Open water lies within three miles. The highest named summit within 15 miles is Nicolai Mountain, about 3,050 ft, 9 miles southeast.
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 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 14×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Basalt. Age: Middle Miocene, 12 to 16 million years old. About 4 mi of the line.
Siltstone, sandstone. Age: Early Miocene to Middle Miocene, 12 to 23 million years old. About 4 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 3 mi of the line.
Sandstone, siltstone. Age: Late Eocene to Early Miocene, 16 to 38 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 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.
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 Knappa reaches the Pacific Ocean by way of Fertile Valley Creek, Knappa Slough, Big Creek Slough, the Prairie Channel, Cathlamet Bay and the Columbia: about 30 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Knappa; river miles along the main stem, rounded.
Knappa has a warm-summer Mediterranean climate. Summer afternoons average 69° in August; winter nights fall to about 37° in February. About 70 inches of rain fall in a normal year.
On November 14 Knappa normally reaches 54° and falls to 40°. The record high is 64°, in 2001; the record low 15°, in 1955. The most rain on this date, 2.78 in, fell in 2015.
Normals 1991–2020 and records since 1887 from the Astoria Area threaded record (Astoria Airport (Port Of), 14 miles west). NOAA, through RCC-ACIS.
