The Ajo 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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94° on Nov. 17, 2020, the hottest reading for this week of the year since 1914. Next is 93° in 2025.
Ajo’s center stands about 1,760 ft above sea level. Within three miles the land runs from 1,220 ft to 2,620 ft, a difference of 1,400 ft: steep hill country. The highest named summit within 15 miles is Growler Peak, about 2,980 ft, 14 miles west.
Under the town center the state geologic map shows Early Tertiary to Late Cretaceous granitic rocks (granite, granodiorite, diorite), from the Late Cretaceous to Early Eocene, 50 to 82 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 12×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gravel, sand. Age: Late Pliocene to Pleistocene, 0.8 to 3 million years old. About 8 mi of the line.
Sand, silt, clay. Age: Pleistocene to Holocene, less than 2 million years old. About 6 mi of the line.
Granite, granodiorite, diorite. Age: Late Oligocene to Middle Miocene, 14 to 26 million years old. About 3 mi of the line.
Basalt, andesite, dacite. Age: Middle Eocene to Late Miocene, 11 to 38 million years old. About 3 mi of the line.
Granite, granodiorite, diorite. Age: Late Cretaceous to Early Eocene, 50 to 82 million years old. About 2 mi of the line.
Metasedimentary, metavolcanic, gneiss. Age: Paleoproterozoic, 1.6 to 1.8 billion 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 Ajo reaches the Gulf of California by way of Tenmile Wash, the Gila and the Colorado: about 270 river miles.
120 miles of the trip are on the Colorado.
Often dry. About 80% 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 Ajo; river miles along the main stem, rounded.
Ajo has a hot desert climate. Summer afternoons average 104° in July; winter nights fall to about 43° in December. About 7 inches of rain fall in a normal year.
On November 14 Ajo normally reaches 78° and falls to 51°. The record high is 91°, in 2017; the record low 34°, in 1916. The most rain on this date, 1.47 in, fell in 2011.
Normals 1991–2020 and records since 1914 at Ajo, here. NOAA, through RCC-ACIS.
