The Big Sky 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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Big Sky’s center stands about 7,170 ft above sea level. Within three miles the land runs from 6,440 ft to 9,270 ft, a difference of 2,830 ft: mountain country. The highest named summit within 15 miles is Lone Mountain, about 11,120 ft, 4 miles west.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 4×. 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: Archean. About 6 mi of the line.
Sandstone, shale, conglomerate. Age: Late Cretaceous, 90 to 100 million years old. About 3 mi of the line.
Sandstone, siltstone, shale. Age: Late Cretaceous, 84 to 87 million years old. About 3 mi of the line.
Sandstone, black-shale. Age: Early Cretaceous, 100 to 113 million years old. About 2 mi of the line.
Sandstone, mudstone. Age: Late Cretaceous, 72 to 84 million years old. About 2 mi of the line.
Gneiss. Age: Archean. 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. 7 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 Big Sky reaches the Gulf of America by way of the Middle Fork West Fork Gallatin, the Gallatin, the Missouri and the Mississippi: about 3,550 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 Big Sky; river miles along the main stem, rounded.
