The Tropic 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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77° on Nov. 15, 2021, the hottest reading for this week of the year since 1979. Next is 72° in 1980.
Tropic’s center stands about 6,300 ft above sea level. Within three miles the land runs from 6,050 ft to 7,510 ft, a difference of 1,460 ft: steep hill country. The highest named summit within 15 miles is Barney Top, about 10,620 ft, 15 miles northeast.
Under the town center the state geologic map shows Alluvium and colluvium (unconsolidated), from the Quaternary, less than 2.6 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 6×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone, mudstone. Age: Late Paleocene to Early Oligocene, 28 to 59 million years old. About 8 mi of the line.
Sandstone, shale. Age: Late Cretaceous, 90 to 100 million years old. About 5 mi of the line.
Unconsolidated. Age: Quaternary, less than 2.6 million years old. About 4 mi of the line.
Sandstone-mudstone, sandstone. Age: Late Cretaceous, 72 to 94 million years old. About 3 mi of the line.
Sandstone-mudstone. Age: Late Cretaceous, 72 to 84 million years old. About 3 mi of the line.
Sandstone-mudstone. Age: Late Cretaceous to Paleocene, 56 to 100 million years old. About 0.7 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 Tropic reaches the Gulf of California by way of the Paria and the Colorado: about 880 river miles.
Lakes on the way: Lake Mead, Lake Mohave and Lake Havasu.
290 miles of the trip are on the Colorado.
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 Tropic; river miles along the main stem, rounded.
Tropic has a cold semi-arid climate. Summer afternoons average 91° in July; winter nights fall to about 15° in January. A normal year brings about 24 inches of snow; with the rain, that comes to about 12 inches of water.
On November 14 Tropic normally reaches 56° and falls to 21°. The record high is 72°, in 1999; the record low 5°, in 2024. The most rain on this date, 0.47 in, fell in 1987.
Normals 1991–2020 and records since 1979 at Kodachrome Basin Park, 9 miles southeast, 500 ft lower. NOAA, through RCC-ACIS.
