The Duncan 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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85° on Nov. 11, 1973, the hottest reading for this week of the year since 1901. Next is 85° in 1999.
Duncan’s center stands about 3,770 ft above sea level. Within three miles the land runs from 3,630 ft to 4,210 ft, a difference of 580 ft: hilly country. The highest named summit within 15 miles is Vanderbilt Peak, about 6,730 ft, 9 miles northeast.
Under the town center the state geologic map shows Pliocene to middle Miocene deposits (conglomerate, sandstone), from the Early Miocene to Pleistocene, 2 to 16 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 8×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Conglomerate, sandstone. Age: Early Miocene to Pleistocene, 2 to 16 million years old. About 11 mi of the line.
Rhyolite. Age: Late Eocene to Early Oligocene, 31 to 36 million years old. About 4 mi of the line.
Basalt, andesite, dacite. Age: Middle Eocene to Late Miocene, 11 to 38 million years old. About 4 mi of the line.
Sand, silt, clay. Age: Pleistocene to Holocene, less than 2 million years old. About 2 mi of the line.
Andesite, basaltic-andesite, basalt. Age: Early Oligocene to Late Oligocene, 26 to 29 million years old. About 2 mi of the line.
Silt, clay. Age: Holocene, less than 10,000 years old. About 1 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 Duncan reaches the Gulf of California by way of the Gila and the Colorado: about 620 river miles.
500 miles of the trip are on the Gila.
Often dry. About 40% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Seldom reaches the sea. Dams and canals now take nearly all of the Colorado before its old delta in Mexico.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Duncan; river miles along the main stem, rounded.
Duncan has a cold semi-arid climate. Summer afternoons average 98° in June; winter nights fall to about 25° in January. About 10 inches of rain fall in a normal year.
On November 14 Duncan normally reaches 70° and falls to 31°. The record high is 85°, in 2017; the record low 15°, in 1975. The most rain on this date, 1.11 in, fell in 1968.
Normals 1991–2020 and records since 1901 at Duncan, here, 110 ft lower. NOAA, through RCC-ACIS.
