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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86° on Nov. 14, 1999, the hottest reading for this week of the year since 1974. Next is 85° in 1989.
St. Mary’s center stands about 450 ft above sea level. Within three miles the land runs from 360 ft to 630 ft, a difference of 270 ft: rolling country. The highest named summit within 15 miles is Madden Hill, about 990 ft, 12 miles west-southwest.
Under the town center the state geologic map shows Chesterian Series (limestone, shale, sandstone), from the Carboniferous, 324 to 359 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 31×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone, sandstone, shale. Age: Late Mississippian, 324 to 331 million years old. About 6 mi of the line.
Limestone, sandstone, shale. Age: Middle Mississippian, 331 to 347 million years old. About 6 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 3 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 3 mi of the line.
Dolostone. Age: Cambrian, 487 to 497 million years old. About 2 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million 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. 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 St. Mary reaches the Gulf of America by way of Saint Laurent Creek, the Old and the Mississippi: about 1,090 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of St. Mary; river miles along the main stem, rounded.
St. Mary has a hot-summer humid continental climate. Summer afternoons average 89° in July; winter nights fall to about 24° in January. About 43 inches of rain fall in a normal year, with about 4 inches of snow.
On November 14 St. Mary normally reaches 56° and falls to 37°. The record high is 86°, in 1999; the record low 9°, in 1986. The most rain on this date, 3.40 in, fell in 1993.
Normals 1991–2020 and records since 1974 at Kaskaskia River Navigation Lock, 8 miles north. NOAA, through RCC-ACIS.
