The Black Rock 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
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83° on Nov. 15, 1964, the hottest reading for this week of the year since 1905. Next is 82° in 1989.
Black Rock’s center stands about 310 ft above sea level. Within three miles the land runs from 240 ft to 430 ft, a difference of 190 ft: gently rolling country. The highest named summit within 15 miles is Cave Hill, about 730 ft, 13 miles west-northwest.
Under the town center the state geologic map shows St. Peter Sanstone and Everton Formation (Middle Ordovician) (sandstone, dolostone), from the Middle Ordovician, 459 to 471 million years old.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 43×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, dolostone. Age: Middle Ordovician, 459 to 471 million years old. About 9 mi of the line.
Coarse-detrital, fine-detrital. Age: Pleistocene, less than 2.6 million years old. About 6 mi of the line.
Sand. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 2 mi of the line.
Coarse-detrital, fine-detrital. Age: Holocene, less than 12,000 years old. About 2 mi of the line.
Sandstone, mudstone. Age: Cretaceous, 66 to 145 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.
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 Black Rock reaches the Gulf of America by way of Fall Creek, the Black River, the White River and the Mississippi: about 950 river miles.
620 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Black Rock; river miles along the main stem, rounded.
Black Rock has a humid subtropical climate. Summer afternoons average 88° in July; winter nights fall to about 28° in January. About 48 inches of rain fall in a normal year, with about 4 inches of snow.
On November 14 Black Rock normally reaches 58° and falls to 39°. The record high is 81°, in 1964; the record low 18°, in 2019. The most rain on this date, 3.48 in, fell in 1957.
Normals 1991–2020 and records since 1905 at Alicia 2 NNE, 13 miles south. NOAA, through RCC-ACIS.
