The Helena Valley Northwest 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 cloudy
Partly cloudy; warmer
Mostly cloudy
Showers likely; cooler
Mostly sunny
Chance of showers
Chance of showers
75° on Nov. 12, 1999, the hottest reading for this week of the year since 1880. Next is 72° in 1990.
Helena Valley Northwest’s center stands about 3,950 ft above sea level. Within three miles the land runs from 3,740 ft to 4,700 ft, a difference of 960 ft: steep hill country. The highest named summit within 15 miles is Greenhorn Mountain, about 7,500 ft, 12 miles west.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Age: Pleistocene to Holocene, less than 1.8 million years old. About 8 mi of the line.
Quartzite, metasiltstone, argillite. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 6 mi of the line.
Metasiltstone, argillite. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 4 mi of the line.
Quartzite, argillite, metasiltstone. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 3 mi of the line.
Sedimentary. Age: Tertiary, 2.6 to 66 million years old. About 2 mi of the line.
Limestone, sandstone. Age: Middle Cambrian, 497 to 521 million years old. About 0.4 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Helena Valley Northwest reaches the Gulf of America by way of Prickly Pear Creek, the Missouri and the Mississippi: about 3,410 river miles.
Lakes on the way: Lake Oahe, Lake Sakakawea, Lake Fort Peck and Lake Sharpe.
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 Helena Valley Northwest; river miles along the main stem, rounded.
Helena Valley Northwest has a cold semi-arid climate. Summer afternoons average 86° in July; winter nights fall to about 13° in January. A normal year brings about 37 inches of snow; with the rain, that comes to about 11 inches of water.
On November 14 Helena Valley Northwest normally reaches 43° and falls to 23°. The record high is 66°, in 2021; the record low −20°, in 1955. The most rain on this date, 0.48 in, fell in 1903.
Normals 1991–2020 and records since 1880 from the Helena Area threaded record (Helena Airport Asos, 9 miles south-southeast). NOAA, through RCC-ACIS.
