The Shamrock 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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Shamrock’s center stands about 1,000 ft above sea level. Within three miles the land runs from 870 ft to 1,070 ft, a difference of 200 ft: gently rolling country.
Under the town center the state geologic map shows Vamoosa Group or Vamoosa Formation (shale, sandstone), from the Carboniferous, 299 to 324 million years old.
The section below crosses 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 62×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 13 mi of the line.
Shale, sandstone, limestone. Age: Carboniferous, 299 to 324 million years old. About 10 mi of the line.
Fine-detrital. Age: Holocene, less than 12,000 years old. About 0.3 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 Shamrock reaches the Gulf of America by way of West Spring Creek, Spring Creek, Little Deep Fork Creek, the Deep Fork, the North Canadian, the Canadian, the Arkansas and the Mississippi: about 1,150 river miles.
Lakes on the way: Murray Lake and Ozark Lake.
600 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Shamrock; river miles along the main stem, rounded.
