The Altona 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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80° on Nov. 16, 2016, the hottest reading for this week of the year since 1893. Next is 78° in 2025.
Altona’s center stands about 5,600 ft above sea level. Within three miles the land runs from 5,300 ft to 7,460 ft, a difference of 2,160 ft: mountain country. The highest named summit within 15 miles is House Rock, about 9,620 ft, 14 miles northwest.
Under the town center the state geologic map shows Colorado Group (shale, limestone), from the Early Cretaceous to Late Cretaceous, 66 to 145 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 5×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Biotite-gneiss, schist, migmatite. Age: Paleoproterozoic, 1.6 to 2.5 billion years old. About 4 mi of the line.
Sand, silt. Age: Quaternary, less than 2.6 million years old. About 4 mi of the line.
Alkali-feldspar-granite, granite. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 4 mi of the line.
Shale. Age: Late Cretaceous, 66 to 100 million years old. About 3 mi of the line.
Granitic, dioritic. Age: Late Cretaceous to Middle Eocene, 40 to 72 million years old. About 3 mi of the line.
Unconsolidated. Age: Quaternary, less than 2.6 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. 7 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 Altona reaches the Gulf of America by way of Left Hand Creek, Saint Vrain Creek, the South Platte, the Platte, the Missouri and the Mississippi: about 2,380 river miles.
1,170 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Altona; river miles along the main stem, rounded.
Altona has a humid subtropical climate. Summer afternoons average 88° in July; winter nights fall to about 21° in December. A normal year brings about 93 inches of snow; with the rain, that comes to about 21 inches of water.
On November 14 Altona normally reaches 55° and falls to 29°. The record high is 78°, in 2025; the record low −2°, in 1916. The most rain on this date, 1.19 in, fell in 1994.
Normals 1991–2020 and records since 1893 at Boulder, 10 miles south, 110 ft lower. NOAA, through RCC-ACIS.
