The Llano 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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Llano’s center stands about 1,030 ft above sea level. Within three miles the land runs from 980 ft to 1,150 ft, a difference of 170 ft: gently rolling country. The highest named summit within 15 miles is Riley Mountains, about 1,810 ft, 10 miles south.
Under the town center the state geologic map shows Packsaddle Schist, from the Proterozoic, 542 to 2,500 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 29×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Paragneiss. Age: Proterozoic, 542 to 2,500 million years old. About 13 mi of the line.
Schist. Age: Proterozoic, 542 to 2,500 million years old. About 6 mi of the line.
Granite. Age: Proterozoic, 542 to 2,500 million years old. About 3 mi of the line.
Hypabyssal-felsic-alkaline. Age: Proterozoic, 542 to 2,500 million years old. About 2 mi of the line.
Limestone, dolostone. Age: Cambrian to Early Ordovician, 471 to 497 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 Llano reaches the Gulf of America by way of the Llano and the Colorado: about 420 river miles.
Lakes on the way: Lake Marble Falls and Lake Lyndon B Johnson.
320 miles of the trip are on the Colorado.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Llano; river miles along the main stem, rounded.
