The Judith Gap 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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75° on Nov. 12, 1999, the hottest reading for this week of the year since 1948. Next is 72° in 1990.
Judith Gap’s center stands about 4,620 ft above sea level. Within three miles the land runs from 4,510 ft to 4,790 ft, a difference of 280 ft: rolling country. The highest named summit within 15 miles is West Peak, about 8,170 ft, 12 miles northeast.
Under the town center the state geologic map shows Judith River Formation (sandstone, shale), from the Late Cretaceous, 72 to 84 million years old.
The section below crosses 12 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. 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 9 mi of the line.
Sandstone, shale. Age: Late Cretaceous, 72 to 84 million years old. About 6 mi of the line.
Limestone. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 2 mi of the line.
Sandstone, shale, bentonite. Age: Late Cretaceous, 66 to 84 million years old. About 1 mi of the line.
Shale. Age: Late Cretaceous, 72 to 84 million years old. About 1 mi of the line.
Shale, sandstone, siltstone. Age: Early Cretaceous to Late Cretaceous, 84 to 113 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. 6 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 Judith Gap reaches the Gulf of America by way of East Fork Roberts Creek, Roberts Creek, Careless Creek, the Musselshell, the Missouri and the Mississippi: about 3,340 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 Judith Gap; river miles along the main stem, rounded.
Judith Gap has a cold semi-arid climate. Summer afternoons average 84° in July; winter nights fall to about 13° in January. A normal year brings about 20 inches of snow; with the rain, that comes to about 13 inches of water.
On November 14 Judith Gap normally reaches 45° and falls to 21°. The record high is 75°, in 1999; the record low −8°, in 1959. The most rain on this date, 0.27 in, fell in 1996.
Normals 1991–2020 and records since 1948 at Harlowton, 17 miles south-southwest, 400 ft lower. NOAA, through RCC-ACIS.
