The Shamrock Colony 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.
Mostly sunny
Mostly sunny; warmer
Mostly sunny
Partly cloudy
Partly cloudy
Partly cloudy; cooler
Showers likely
76° on Nov. 16, 2001, the hottest reading for this week of the year since 1881. Next is 75° in 1953.
Shamrock Colony’s center stands about 1,400 ft above sea level. Within three miles the land runs from 1,360 ft to 1,460 ft, a difference of 100 ft: gently rolling country.
Under the town center the state geologic map shows Pierre Shale (shale, bentonite), from the Late Cretaceous, 66 to 100 million years old.
The section below crosses 2 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 33×. 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, bentonite. Age: Late Cretaceous, 66 to 100 million years old. About 21 mi of the line.
Chalk, marlstone, shale. Age: Late Cretaceous, 66 to 100 million years old. About 3 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 Shamrock Colony reaches the Gulf of America by way of Shue Creek, the James, the Missouri and the Mississippi: about 2,210 river miles.
1,170 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Shamrock Colony; river miles along the main stem, rounded.
Shamrock Colony has a hot-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 6° in January. A normal year brings about 44 inches of snow; with the rain, that comes to about 23 inches of water.
On November 14 Shamrock Colony normally reaches 45° and falls to 23°. The record high is 74°, in 2025; the record low −18°, in 1959. The most rain on this date, 0.44 in, fell in 1928.
Normals 1991–2020 and records since 1881 from the Huron Area threaded record (Huron Regional Airport, 21 miles southwest, 120 ft lower). NOAA, through RCC-ACIS.
