The Alzada 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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Alzada’s center stands about 3,440 ft above sea level. Within three miles the land runs from 3,400 ft to 3,710 ft, a difference of 310 ft: rolling country. The highest named summit within 15 miles is Branaman Mountain, about 4,240 ft, 13 miles south.
Under the town center the state geologic map shows Belle Fourche Formation (black-shale, sandstone), from the Late Cretaceous, 94 to 100 million years old.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 26×. 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, 90 to 94 million years old. About 5 mi of the line.
Black-shale, sandstone. Age: Late Cretaceous, 94 to 100 million years old. About 4 mi of the line.
Shale. Age: Early Cretaceous to Late Cretaceous, 66 to 145 million years old. About 3 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 3 mi of the line.
Sandstone, claystone. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 3 mi of the line.
Sandstone, shale. Age: Early Cretaceous, 100 to 145 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. 2 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 Alzada reaches the Gulf of America by way of the Little Missouri, the Missouri and the Mississippi: about 3,140 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 Alzada; river miles along the main stem, rounded.
