The Letts 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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−2° on Nov. 17, 1959, the coldest reading for this week of the year since 1900. Next is 2° in 1940.
Letts’s center stands about 660 ft above sea level. Within three miles the land runs from 630 ft to 760 ft, a difference of 130 ft: gently rolling country.
Under the town center the state geologic map shows Cedar Valley Group (limestone, dolostone), from the Middle Devonian to Late Devonian, 374 to 388 million years old.
The section below crosses 7 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.
Limestone, dolostone. Age: Middle Devonian to Late Devonian, 374 to 388 million years old. About 12 mi of the line.
Shale, siltstone. Age: Late Devonian, 359 to 374 million years old. About 8 mi of the line.
Dolostone, limestone. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 1 mi of the line.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 0.9 mi of the line.
Shale, limestone, dolostone. Age: Late Devonian, 374 to 384 million years old. About 0.6 mi of the line.
Dolostone, limestone. Age: Middle Devonian, 384 to 394 million years old. About 0.6 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Letts reaches the Gulf of America by way of Indian Creek, the Iowa and the Mississippi: about 1,440 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Letts; river miles along the main stem, rounded.
Letts has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 11° in January. A normal year brings about 31 inches of snow; with the rain, that comes to about 39 inches of water.
On November 14 Letts normally reaches 49° and falls to 27°. The record high is 76°, in 1958; the record low 0°, in 1959. The most rain on this date, 0.94 in, fell in 1926.
Normals 1991–2020 and records since 1900 at Columbus Junction, 7 miles west-southwest. NOAA, through RCC-ACIS.
