The St. Marys 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.
Mostly sunny
Partly cloudy; warmer
Mostly sunny
Mostly sunny
Partly cloudy
Mostly sunny
Chance of showers
81° on Nov. 13, 1999, the hottest reading for this week of the year since 1878. Next is 76° in 2001.
St. Marys’s center stands about 1,030 ft above sea level. Within three miles the land runs from 840 ft to 1,040 ft, a difference of 200 ft: rolling country.
Under the town center the state geologic map shows Lower Cherokee Group and Raccoon Creek Group (shale, sandstone, siltstone), from the Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million 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 57×. 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, siltstone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 8 mi of the line.
Shale, limestone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 7 mi of the line.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 6 mi of the line.
Limestone, shale. Age: Middle Pennsylvanian to Late Pennsylvanian, 299 to 315 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 St. Marys reaches the Gulf of America by way of the South River, the Des Moines and the Mississippi: about 1,530 river miles.
Lake on the way: Roberts Creek.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of St. Marys; river miles along the main stem, rounded.
St. Marys has a hot-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 14° in January. A normal year brings about 36 inches of snow; with the rain, that comes to about 36 inches of water.
On November 14 St. Marys normally reaches 49° and falls to 31°. The record high is 74°, in 2025; the record low −1°, in 1959. The most rain on this date, 0.86 in, fell in 1947.
Normals 1991–2020 and records since 1878 from the Des Moines Area threaded record (Des Moines International Airport, 16 miles north-northeast). NOAA, through RCC-ACIS.
