The Algona 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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Algona’s center stands about 1,190 ft above sea level. Within three miles the land runs from 1,110 ft to 1,250 ft, a difference of 140 ft: gently rolling country.
Under the town center the state geologic map shows Dakata and Windrow Formations (sandstone, shale), from the Early Cretaceous to Late Cretaceous, 94 to 113 million 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 64×. 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, shale. Age: Early Cretaceous to Late Cretaceous, 94 to 113 million years old. About 20 mi of the line.
Shale, limestone, dolostone. Age: Late Devonian, 374 to 384 million years old. About 3 mi of the line.
Shale, siltstone. Age: Late Devonian, 359 to 374 million years old. About 1 mi of the line.
Dolostone, limestone, siltstone. Age: Early Mississippian, 347 to 359 million years old. About 0.5 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 Algona reaches the Gulf of America by way of the Des Moines and the Mississippi: about 1,710 river miles.
Lakes on the way: Roberts Creek and Big Creek Pounding Area.
1,330 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Algona; river miles along the main stem, rounded.
