The Castle Rock 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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Castle Rock’s center stands about 820 ft above sea level. Within three miles the land runs from 730 ft to 1,140 ft, a difference of 410 ft: hilly country. The highest named summit within 15 miles is Pine Hill, about 1,140 ft, 9 miles northeast.
Under the town center the state geologic map shows Prairie du Chien Group (dolostone), from the Early Ordovician, 471 to 487 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 34×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 9 mi of the line.
Dolostone. Age: Ordovician, 445 to 487 million years old. About 7 mi of the line.
Sandstone. Age: Cambrian, 487 to 542 million years old. About 5 mi of the line.
Sandstone. Age: Ordovician, 445 to 487 million years old. About 4 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 Castle Rock reaches the Gulf of America by way of the Blue River, the Wisconsin and the Mississippi: about 1,660 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Castle Rock; river miles along the main stem, rounded.
