The Round 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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Round Mountain’s center stands about 1,280 ft above sea level. Within three miles the land runs from 1,150 ft to 1,580 ft, a difference of 430 ft: hilly country. The highest named summit within 15 miles is Smith Mountains, about 1,800 ft, 15 miles west.
Under the town center the state geologic map shows Hensell Sand (limestone), from the Early Cretaceous, 100 to 145 million years old.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 20×. 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, marlstone. Age: Early Cretaceous, 100 to 145 million years old. About 11 mi of the line.
Limestone. Age: Early Cretaceous, 100 to 145 million years old. About 8 mi of the line.
Limestone. Age: Early Cretaceous, 100 to 145 million years old. About 2 mi of the line.
Sandstone. Age: Middle Cambrian, 497 to 521 million years old. About 1 mi of the line.
Granite. Age: Proterozoic, 542 to 2,500 million years old. About 1 mi of the line.
Limestone. Age: Early Cretaceous, 100 to 113 million years old. About 0.8 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Round Mountain reaches the Gulf of America by way of Cypress Creek, the Pedernales and the Colorado: about 380 river miles.
Lake on the way: Lake Marble Falls.
320 miles of the trip are on the Colorado.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Round Mountain; river miles along the main stem, rounded.
