The Ismay 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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77° on Nov. 12, 1999, the hottest reading for this week of the year since 1910. Next is 72° in 1953.
Ismay’s center stands about 2,530 ft above sea level. Within three miles the land runs from 2,480 ft to 2,770 ft, a difference of 290 ft: rolling country. The highest named summit within 15 miles is Henry Woods Mountain, about 3,260 ft, 14 miles west-southwest.
The section below crosses 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 29×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, shale. Age: Early Paleocene to Middle Paleocene, 59 to 66 million years old. About 21 mi of the line.
Shale, siltstone, bentonite. Age: Early Paleocene, 62 to 66 million years old. About 2 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 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.
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 Ismay reaches the Gulf of America by way of O'Fallon Creek, the Yellowstone, the Missouri and the Mississippi: about 2,920 river miles.
Lakes on the way: Lake Oahe, Lake Sakakawea, Lake Sharpe and Lake Francis Case.
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 Ismay; river miles along the main stem, rounded.
Ismay has a cold semi-arid climate. Summer afternoons average 86° in July; winter nights fall to about 6° in January. A normal year brings about 34 inches of snow; with the rain, that comes to about 16 inches of water.
On November 14 Ismay normally reaches 44° and falls to 19°. The record high is 69°, in 1999; the record low −24°, in 1955. The most rain on this date, 0.65 in, fell in 1964.
Normals 1991–2020 and records since 1910 at Plevna, 14 miles east-southeast, 250 ft higher. NOAA, through RCC-ACIS.
