The Onalaska 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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Onalaska’s center stands about 500 ft above sea level. Within three miles the land runs from 420 ft to 870 ft, a difference of 450 ft: hilly country. The highest named summit within 15 miles is Lookout Peak, about 3,460 ft, 15 miles east-northeast.
Under the town center the state geologic map shows Alluvium (silt, sand), from the Holocene, less than 12,000 years old.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. 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 11 mi of the line.
Gravel, sand. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Silt, sand. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Andesite, basaltic-andesite. Age: Late Eocene, 34 to 38 million years old. About 3 mi of the line.
Siltstone, sandstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 2 mi of the line.
Sand, gravel. Age: Pleistocene, 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 Onalaska reaches the Pacific Ocean by way of the South Fork Newaukum, the Newaukum and the Chehalis: about 100 river miles.
80 miles of the trip are on the Chehalis.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Onalaska; river miles along the main stem, rounded.
