The O'Brien 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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65° on Nov. 15, 2025, the hottest reading for this week of the year since 1943. Next is 64° in 1981.
O'Brien’s center stands about 1,320 ft above sea level. Within three miles the land runs from 1,250 ft to 1,390 ft, a difference of 140 ft: gently rolling country.
Under the town center the state geologic map shows Granitoid intrusion (granitic), from the Neoarchean, 2.5 to 2.8 billion years old.
The section below crosses 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granitic. Age: Neoarchean, 2.5 to 2.8 billion years old. About 11 mi of the line.
Metabasalt, greenstone. Age: Neoarchean, 2.5 to 2.8 billion years old. About 7 mi of the line.
Felsic-volcanic. Age: Neoarchean, 2.5 to 2.8 billion years old. About 3 mi of the line.
Granitic. Age: Neoarchean, 2.5 to 2.8 billion 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.
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 O'Brien reaches Hudson Bay by way of Darrigans Creek, O'Brien Creek, the Blackduck, the Red Lake, the Red River of the North and the Nelson: about 1,180 river miles. Past the border it runs north through Canada to Hudson Bay.
Lakes on the way: Upper Red Lake and Lake Winnipeg.
400 miles of the trip are on the Nelson.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of O'Brien; river miles along the main stem, rounded.
O'Brien has a warm-summer humid continental climate. Summer afternoons average 77° in July; winter nights fall to about −3° in January. About 23 inches of rain fall in a normal year.
On November 14 O'Brien normally reaches 35° and falls to 21°. The record high is 64°, in 2016; the record low −11°, in 1959. The most rain on this date, 0.81 in, fell in 1944.
Normals 1991–2020 and records since 1943 at Red Lake Indian Agcy, 13 miles west-northwest, 100 ft lower. NOAA, through RCC-ACIS.
