The Seneca 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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Mostly sunny; warmer
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75° on Nov. 11, 2022, the hottest reading for this week of the year since 1941. Next is 74° in 2020.
Seneca’s center stands about 510 ft above sea level. Within three miles the land runs from 480 ft to 690 ft, a difference of 210 ft: rolling country.
Under the town center the state geologic map shows Carbondale Formation (shale, sandstone, coal), from the Middle Pennsylvanian to Late Pennsylvanian, 304 to 315 million years old.
The section below crosses 3 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.
Shale, sandstone, coal. Age: Middle Pennsylvanian to Late Pennsylvanian, 304 to 315 million years old. About 14 mi of the line.
Shale, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 7 mi of the line.
Sandstone, limestone, dolostone. Age: Middle Ordovician to Late Ordovician, 454 to 468 million years old. About 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 Seneca reaches the Gulf of America by way of the Illinois and the Mississippi: about 1,440 river miles.
Lake on the way: Peoria Lake.
1,190 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Seneca; river miles along the main stem, rounded.
Seneca has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 14° in January. A normal year brings about 25 inches of snow; with the rain, that comes to about 39 inches of water.
Normals 1991–2020 and records since 1941 at Marseilles Lock/Dam, 8 miles west. NOAA, through RCC-ACIS.
