The Zortman 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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Zortman’s center stands about 4,050 ft above sea level. Within three miles the land runs from 3,580 ft to 5,540 ft, a difference of 1,960 ft: steep hill country. The highest named summit within 15 miles is Antoine Butte, about 5,730 ft, 3 miles west-northwest.
Under the town center the state geologic map shows Kootenai Formation through Ellis Group: Kootenai, Morrison, and Ellis Group (sandstone, limestone, shale), from the Middle Jurassic to Early Cretaceous, 100 to 172 million years old.
The section below crosses 18 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.
Shale. Age: Late Cretaceous, 72 to 84 million years old. About 4 mi of the line.
Age: Tertiary, 2.6 to 66 million years old. About 3 mi of the line.
Age: Late Miocene to Holocene, less than 7.2 million years old. About 3 mi of the line.
Shale, sandstone. Age: Early Cretaceous to Late Cretaceous, 94 to 113 million years old. About 2 mi of the line.
Shale, sandstone, limestone. Age: Late Cretaceous, 72 to 100 million years old. About 2 mi of the line.
Limestone, dolostone, black-shale. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 12 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 Zortman reaches the Gulf of America by way of Camp Creek, C K Creek, the Missouri and the Mississippi: about 3,090 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 Zortman; river miles along the main stem, rounded.
