The St. Mary 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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St. Mary’s center stands about 4,630 ft above sea level. Within three miles the land runs from 4,470 ft to 6,280 ft, a difference of 1,810 ft: steep hill country. The highest named summit within 15 miles is Mount Siyeh, about 9,910 ft, 10 miles west.
Under the town center the state geologic map shows Marias River Formation (shale, dolostone, limestone), from the Late Cretaceous, 84 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 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.
Sandstone, siltstone, mudstone. Age: Late Cretaceous, 66 to 84 million years old. About 7 mi of the line.
Metasiltstone, argillite, quartzite. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 6 mi of the line.
Shale, dolostone, limestone. Age: Late Cretaceous, 84 to 100 million years old. About 4 mi of the line.
Quartzite, argillite, metasiltstone. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 3 mi of the line.
Sandstone, siltstone, shale. Age: Late Cretaceous, 72 to 87 million years old. About 2 mi of the line.
Quartzite, metasiltstone, argillite. Age: Mesoproterozoic, 1 to 1.6 billion 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. 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 St. Mary reaches Hudson Bay by way of Divide Creek, the Saint Mary, the Oldman, the South Saskatchewan, the Saskatchewan and the Nelson: about 1,750 river miles. Past the border it runs north through Canada to Hudson Bay.
Lake on the way: Lake Winnipeg.
500 miles of the trip are on the South Saskatchewan.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of St. Mary; river miles along the main stem, rounded.
