The Fort Clark Springs 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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Fort Clark Springs’s center stands about 1,150 ft above sea level. Within three miles the land runs from 1,080 ft to 1,230 ft, a difference of 150 ft: gently rolling country. The highest named summit within 15 miles is Turkey Mountain, about 1,790 ft, 14 miles east-northeast.
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 38×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gravel. Age: Late Pliocene to Pleistocene, less than 3.6 million years old. About 12 mi of the line.
Black-shale, siltstone. Age: Late Cretaceous, 66 to 100 million years old. About 5 mi of the line.
Limestone. Age: Late Cretaceous, 66 to 100 million years old. About 5 mi of the line.
Limestone. Age: Early Cretaceous, 100 to 145 million years old. About 2 mi of the line.
Marlstone, chalk. Age: Late Cretaceous, 66 to 100 million years old. About 0.9 mi of the line.
Marl. Age: Late Cretaceous, 66 to 100 million years old. About 0.5 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 Fort Clark Springs reaches the Gulf of America by way of Las Moras Creek and the Rio Grande: about 550 river miles.
Lake on the way: Paz Ramirez Lake.
270 miles of the trip are on the Rio Grande.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Fort Clark Springs; river miles along the main stem, rounded.
