The Olla 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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Olla’s center stands about 150 ft above sea level. Within three miles the land runs from 80 ft to 210 ft, a difference of 130 ft: gently rolling country. The highest named summit within 15 miles is Bald Hill, about 340 ft, 14 miles east.
Under the town center the state geologic map shows Intermediate Terraces (clay, silt), from the Pleistocene, less than 2.6 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 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 7 mi of the line.
Clay, silt, sand. Age: Pleistocene, less than 2.6 million years old. About 6 mi of the line.
Clay. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Clay, silt. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Clay, sand, lignite. Age: Eocene, 34 to 56 million years old. About 3 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 Olla reaches the Gulf of America by way of Chickasaw Creek, Castor Creek, the Little River, the Black River, the Red River, the Atchafalaya and the Lower Atchafalaya: about 320 river miles.
Lake on the way: Catahoula Lake.
100 miles of the trip are on the Atchafalaya.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Olla; river miles along the main stem, rounded.
