The Olney 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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Olney’s center stands about 1,190 ft above sea level. Within three miles the land runs from 1,150 ft to 1,260 ft, a difference of 110 ft: gently rolling country.
Under the town center the state geologic map shows Archer City Formation (black-shale), from the Permian, 252 to 299 million years old.
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 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Black-shale. Age: Permian, 252 to 299 million years old. About 14 mi of the line.
Sandstone. Age: Carboniferous to Permian, 252 to 324 million years old. About 5 mi of the line.
Coarse-detrital, fine-detrital. Age: Quaternary, less than 2.6 million years old. About 3 mi of the line.
Fine-detrital, coarse-detrital. Age: Holocene, less than 12,000 years old. About 1 mi of the line.
Sand. Age: Pleistocene to Holocene, less than 2.6 million years old. About 0.4 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 Olney reaches the Gulf of America by way of Mud Creek, Salt Creek and the Brazos: about 780 river miles.
Lakes on the way: Possum Kingdom Lake and Lake Granbury.
550 miles of the trip are on the Brazos.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Olney; river miles along the main stem, rounded.
