The Calhan 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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Calhan’s center stands about 6,530 ft above sea level. Within three miles the land runs from 6,340 ft to 6,970 ft, a difference of 630 ft: hilly country. The highest named summit within 15 miles is Rattlesnake Butte, about 7,410 ft, 12 miles west-northwest.
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 17×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gravel, unconsolidated. Age: Pleistocene, 0.2 to 1.6 million years old. About 10 mi of the line.
Arkose, conglomerate, shale. Age: Paleocene to Eocene, 34 to 66 million years old. About 6 mi of the line.
Arkose, shale, mudstone. Age: Late Cretaceous to Paleocene, 56 to 100 million years old. About 3 mi of the line.
Unconsolidated. Age: Quaternary, less than 2.6 million years old. About 2 mi of the line.
Sandstone, claystone. Age: Oligocene, 23 to 34 million years old. About 2 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 Calhan reaches the Gulf of America by way of Big Sandy Creek, the Arkansas and the Mississippi: about 1,890 river miles.
Lakes on the way: Murray Lake and Ozark Lake.
800 miles of the trip are on the Arkansas.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Calhan; river miles along the main stem, rounded.
