The Lewistown 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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−29° on Nov. 16, 1959, the coldest reading for this week of the year since 1896. Next is −24° in 1986.
Lewistown’s center stands about 3,950 ft above sea level. Within three miles the land runs from 3,840 ft to 4,340 ft, a difference of 500 ft: hilly country. The highest named summit within 15 miles is Judith Peak, about 6,410 ft, 14 miles northeast.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 10×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Age: Late Miocene to Holocene, less than 7.2 million years old. About 11 mi of the line.
Limestone, dolostone, black-shale. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 5 mi of the line.
Shale, sandstone. Age: Early Cretaceous, 100 to 113 million years old. About 3 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 2 mi of the line.
Limestone, mudstone, sandstone. Age: Middle Jurassic to Late Jurassic, 145 to 172 million years old. About 1 mi of the line.
Black-shale, limestone, sandstone. Age: Middle Mississippian to Late Mississippian, 324 to 347 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 3 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 Lewistown reaches the Gulf of America by way of Little Casino Creek, Big Spring Creek, the Judith, the Missouri and the Mississippi: about 3,230 river miles.
Lakes on the way: Lake Oahe, Lake Sakakawea, Lake Fort Peck and Lake Sharpe.
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 Lewistown; river miles along the main stem, rounded.
Lewistown has a warm-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 13° in January. About 17 inches of rain fall in a normal year.
On November 14 Lewistown normally reaches 44° and falls to 21°. The record high is 72°, in 1999; the record low −21°, in 1955. The most rain on this date, 0.25 in, fell in 2011.
Normals 1991–2020 and records since 1896 at Lewistown Airport, here, 180 ft higher. NOAA, through RCC-ACIS.
