The Spearsville 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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Spearsville’s center stands about 200 ft above sea level. Within three miles the land runs from 110 ft to 260 ft, a difference of 150 ft: gently rolling country.
Under the town center the state geologic map shows Cockfield Formation (clay, silt, sand), from the Eocene, 34 to 56 million years old.
The section below crosses 4 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.
Clay, silt, sand. Age: Eocene, 34 to 56 million years old. About 13 mi of the line.
Sand, clay. Age: Middle Eocene, 38 to 48 million years old. About 6 mi of the line.
Clay. Age: Holocene, less than 12,000 years old. About 5 mi of the line.
Clay, marl. Age: Eocene, 34 to 56 million years old. About 0.1 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 Spearsville reaches the Gulf of America by way of Tenmile Creek, Cornie Bayou, the Bayou D'Arbonne, the Ouachita, the Black River, the Red River, the Atchafalaya and the Lower Atchafalaya: about 400 river miles.
Lake on the way: Bayou D'Arbonne Lake.
130 miles of the trip are on the Ouachita.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Spearsville; river miles along the main stem, rounded.
