The Roy 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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Roy’s center stands about 3,490 ft above sea level. Within three miles the land runs from 3,390 ft to 3,830 ft, a difference of 440 ft: hilly country. The highest named summit within 15 miles is Judith Peak, about 6,410 ft, 15 miles west-southwest.
Under the town center the state geologic map shows Bearpaw Formation (shale), from the Late Cretaceous, 72 to 84 million years old.
The section below crosses 10 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 13 mi of the line.
Sandstone, shale. Age: Late Cretaceous, 72 to 84 million years old. About 4 mi of the line.
Shale, sandstone. Age: Early Cretaceous to Late Cretaceous, 94 to 113 million years old. About 2 mi of the line.
Sandstone, sandstone-mudstone. Age: Late Cretaceous, 72 to 87 million years old. About 1 mi of the line.
Granitic. Age: Cretaceous to Tertiary, 2.6 to 145 million years old. About 1 mi of the line.
Age: Late Miocene to Holocene, less than 7.2 million 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. 4 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 Roy reaches the Gulf of America by way of Box Elder Creek, Flatwillow Creek, the Musselshell, the Missouri and the Mississippi: about 3,230 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 Roy; river miles along the main stem, rounded.
