The Silvis 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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−1° on Nov. 15, 1959, the coldest reading for this week of the year since 1871. Next is 3° in 1933.
Silvis’s center stands about 600 ft above sea level. Within three miles the land runs from 550 ft to 720 ft, a difference of 170 ft: gently rolling country.
Under the town center the state geologic map shows Muscatatuck Group (limestone), from the Middle Devonian, 384 to 394 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.
Shale, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 10 mi of the line.
Dolostone, mudstone. Age: Silurian, 425 to 434 million years old. About 6 mi of the line.
Limestone. Age: Middle Devonian, 384 to 394 million years old. About 3 mi of the line.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 2 mi of the line.
Shale. Age: Middle Devonian to Late Devonian, 359 to 388 million years old. About 1 mi of the line.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 0.9 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 Silvis reaches the Gulf of America by way of Sugar Creek and the Mississippi: about 1,470 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Silvis; river miles along the main stem, rounded.
Silvis has a hot-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 15° in January. A normal year brings about 36 inches of snow; with the rain, that comes to about 38 inches of water.
On November 14 Silvis normally reaches 50° and falls to 31°. The record high is 75°, in 1971; the record low 0°, in 1959. The most rain on this date, 1.16 in, fell in 1968.
Normals 1991–2020 and records since 1871 from the Moline Area threaded record (Moline Quad City International Airport, 7 miles southwest). NOAA, through RCC-ACIS.
