The Jamestown 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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73° on Nov. 14, 1999, the hottest reading for this week of the year since 1937. Next is 71° in 1953.
Jamestown’s center stands about 930 ft above sea level. Within three miles the land runs from 820 ft to 1,010 ft, a difference of 190 ft: gently rolling country. The highest named summit within 15 miles is Platte Mounds, about 1,470 ft, 14 miles north-northeast.
Under the town center the state geologic map shows Sinnipee Group (dolostone), from the Ordovician, 445 to 487 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 40×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Dolostone. Age: Ordovician, 445 to 487 million years old. About 18 mi of the line.
Dolostone, sandstone. Age: Early Ordovician to Late Ordovician, 454 to 487 million years old. About 2 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 2 mi of the line.
Shale, dolostone. Age: Late Ordovician, 447 to 454 million years old. About 2 mi of the line.
Shale, dolostone. Age: Ordovician, 445 to 487 million years old. About 0.8 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 Jamestown reaches the Gulf of America by way of the Menominee and the Mississippi: about 1,560 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Jamestown; river miles along the main stem, rounded.
Jamestown has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 10° in January. A normal year brings about 36 inches of snow; with the rain, that comes to about 39 inches of water.
On November 14 Jamestown normally reaches 46° and falls to 30°. The record high is 73°, in 1999; the record low 12°, in 1959. The most rain on this date, 0.75 in, fell in 2024.
Normals 1991–2020 and records since 1937 at Dubuque L&D 11, 6 miles west-southwest, 310 ft lower. NOAA, through RCC-ACIS.
