The Spiro 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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87° on Nov. 16, 2016, the hottest reading for this week of the year since 1882. Next is 86° in 1955.
Spiro’s center stands about 490 ft above sea level. Within three miles the land runs from 410 ft to 580 ft, a difference of 170 ft: gently rolling country. The highest named summit within 15 miles is Cavanal Mountain, about 2,380 ft, 12 miles south-southwest.
Under the town center the state geologic map shows McAlester and Hartshorne Formations (shale, sandstone), from the Carboniferous, 299 to 324 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 19×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Fine-detrital. Age: Holocene, less than 12,000 years old. About 7 mi of the line.
Shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 7 mi of the line.
Shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 4 mi of the line.
Shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 3 mi of the line.
Coarse-detrital, fine-detrital. Age: Pleistocene, less than 2.6 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.
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 Spiro reaches the Gulf of America by way of the Poteau, the Arkansas and the Mississippi: about 950 river miles.
Lakes on the way: Murray Lake and Ozark Lake.
600 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Spiro; river miles along the main stem, rounded.
Spiro has a humid subtropical climate. Summer afternoons average 94° in July; winter nights fall to about 30° in January. About 47 inches of rain fall in a normal year, with about 3 inches of snow.
On November 14 Spiro normally reaches 64° and falls to 40°. The record high is 82°, in 2011; the record low 19°, in 1963. The most rain on this date, 2.81 in, fell in 1994.
Normals 1991–2020 and records since 1882 from the Fort Smith Area threaded record (Fort Smith Regional Airport, 16 miles east-northeast). NOAA, through RCC-ACIS.
