The Donaldson 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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Donaldson’s center stands about 920 ft above sea level. Within three miles the land runs from 750 ft to 1,660 ft, a difference of 910 ft: steep hill country. The highest named summit within 15 miles is Big Mountain, about 1,830 ft, 13 miles north.
Under the town center the state geologic map shows Llewellyn Formation (sandstone), from the Carboniferous, 299 to 324 million years old.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 15×. 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. Age: Carboniferous, 299 to 324 million years old. About 6 mi of the line.
Shale, siltstone, sandstone. Age: Carboniferous, 324 to 359 million years old. About 5 mi of the line.
Sandstone. Age: Carboniferous, 299 to 324 million years old. About 5 mi of the line.
Siltstone, shale. Age: Late Devonian, 359 to 384 million years old. About 2 mi of the line.
Siltstone, mudstone. Age: Late Devonian, 359 to 384 million years old. About 1 mi of the line.
Shale. Age: Silurian, 422 to 445 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 5 smaller units along the line are not listed.
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 Donaldson reaches Chesapeake Bay and the Atlantic Ocean by way of Good Spring Creek, Swatara Creek and the Susquehanna: about 130 river miles.
Lake on the way: Lake Aldred.
65 miles of the trip are on Swatara Creek.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Donaldson; river miles along the main stem, rounded.
