The Irwinton 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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Irwinton’s center stands about 450 ft above sea level. Within three miles the land runs from 260 ft to 490 ft, a difference of 230 ft: rolling country.
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 63×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sand, clay. Age: Cretaceous to Tertiary, 2.6 to 145 million years old. About 10 mi of the line.
Clay. Age: Eocene, 34 to 56 million years old. About 10 mi of the line.
Sand. Age: Eocene, 34 to 56 million years old. About 2 mi of the line.
Fine-detrital. Age: Quaternary, less than 2.6 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 Irwinton reaches the Atlantic Ocean by way of Town Branch, Big Sandy Creek, the Oconee and the Altamaha: about 230 river miles.
130 miles of the trip are on the Altamaha.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Irwinton; river miles along the main stem, rounded.
