The Twin Creeks 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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72° on Nov. 13, 1999, the hottest reading for this week of the year since 1964. Next is 65° in 1990.
Twin Creeks’s center stands about 3,430 ft above sea level. Within three miles the land runs from 3,390 ft to 5,730 ft, a difference of 2,340 ft: mountain country. The highest named summit within 15 miles is Mosquito Peak, about 7,980 ft, 14 miles northwest.
Under the town center the state geologic map shows Upper Missoula Group: McNamara, Bonner, and Mount Shields Formations; locally includes lower Libby Formation in northwestern Montana (metasiltstone, argillite, quartzite), from the Mesoproterozoic, 1 to 1.6 billion 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 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.
Quartzite, argillite, metasiltstone. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 8 mi of the line.
Metasiltstone, argillite, quartzite. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 7 mi of the line.
Sedimentary. Age: Tertiary, 2.6 to 66 million years old. About 7 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 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.
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 Twin Creeks reaches the Pacific Ocean by way of the Blackfoot, the Clark Fork, the Pend Oreille and the Columbia: about 1,090 river miles.
Lakes on the way: Lake Pend Oreille, Lake Umatilla and Noxon Rapids Reservoir.
460 miles of the trip are on the Columbia.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Twin Creeks; river miles along the main stem, rounded.
Twin Creeks has a warm-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 8° in January. A normal year brings about 52 inches of snow; with the rain, that comes to about 15 inches of water.
On November 14 Twin Creeks normally reaches 40° and falls to 17°. The record high is 65°, in 1999; the record low −6°, in 1978. The most rain on this date, 0.49 in, fell in 1986.
Normals 1991–2020 and records since 1964 at Potomac, 8 miles east-southeast, 260 ft higher. NOAA, through RCC-ACIS.
