The Marion 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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Marion’s center stands about 190 ft above sea level. Within three miles the land runs from 120 ft to 240 ft, a difference of 120 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 6 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 12 mi of the line.
Clay. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Clay. Age: Pleistocene, less than 2.6 million years old. About 3 mi of the line.
Silt, clay. Age: Holocene, less than 12,000 years old. About 3 mi of the line.
Clay, silt. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Clay, silt, sand. Age: Pleistocene, 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 Marion reaches the Gulf of America by way of Big Creek, the Bayou de Loutre, the Ouachita, the Black River, the Red River, the Atchafalaya and the Lower Atchafalaya: about 380 river miles.
150 miles of the trip are on the Ouachita.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Marion; river miles along the main stem, rounded.
