The Southwest Madison 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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76° on Nov. 11, 2020, the hottest reading for this week of the year since 1840. Next is 74° in 2009.
Southwest Madison’s center stands about 740 ft above sea level. Within three miles the land runs from 600 ft to 2,040 ft, a difference of 1,440 ft: steep hill country. The highest named summit within 15 miles is Rising Mountain, about 2,300 ft, 15 miles southwest.
Under the town center the state geologic map shows Bloomsburg and Mifflintown Formations, undivided (shale), from the Silurian, 422 to 445 million years old.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 12×. 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. Age: Ordovician, 445 to 487 million years old. About 7 mi of the line.
Shale. Age: Silurian, 422 to 445 million years old. About 4 mi of the line.
Shale. Age: Silurian, 422 to 445 million years old. About 3 mi of the line.
Quartzite. Age: Silurian, 422 to 445 million years old. About 3 mi of the line.
Limestone. Age: Silurian to Devonian, 359 to 445 million years old. About 3 mi of the line.
Shale, sandstone. Age: Silurian, 422 to 445 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 4 smaller units along the line are not listed.
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 Southwest Madison reaches Chesapeake Bay and the Atlantic Ocean by way of Sherman Creek and the Susquehanna: about 130 river miles.
Lake on the way: Lake Aldred.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Southwest Madison; river miles along the main stem, rounded.
Southwest Madison has a hot-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 21° in January. A normal year brings about 28 inches of snow; with the rain, that comes to about 48 inches of water.
Normals 1991–2020 and records since 1840 at Carlisle Water Plant, 16 miles east-southeast, 310 ft lower. NOAA, through RCC-ACIS.
