The South Mountain 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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South Mountain’s center stands about 1,020 ft above sea level. Within three miles the land runs from 760 ft to 1,050 ft, a difference of 290 ft: rolling country. The highest named summit within 15 miles is Shell Mountains, about 1,210 ft, 12 miles southwest.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 42×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone, marl. Age: Early Cretaceous, 100 to 145 million years old. About 7 mi of the line.
Limestone, shale. Age: Early Cretaceous, 100 to 145 million years old. About 6 mi of the line.
Claystone. Age: Early Cretaceous, 100 to 145 million years old. About 6 mi of the line.
Claystone, limestone. Age: Early Cretaceous, 100 to 145 million years old. About 3 mi of the line.
Fine-detrital, coarse-detrital. Age: Holocene, less than 12,000 years old. About 2 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 South Mountain reaches the Gulf of America by way of South Greenbriar Creek, the Leon, the Little River and the Brazos: about 490 river miles.
Lake on the way: Belton Lake.
320 miles of the trip are on the Brazos.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of South Mountain; river miles along the main stem, rounded.
