The St. Johns 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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93° on Nov. 12, 1999, the hottest reading for this week of the year since 1895. Next is 92° in 1967.
St. Johns’s center stands about 1,010 ft above sea level. Within three miles the land runs from 980 ft to 1,280 ft, a difference of 300 ft: rolling country. The highest named summit within 15 miles is Montezuma Peak, about 4,200 ft, 9 miles south.
Under the town center the state geologic map shows Holocene surficial deposits (silt, clay), from the Holocene, less than 10,000 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.
Silt, clay. Age: Holocene, less than 10,000 years old. About 6 mi of the line.
Sand, gravel. Age: Holocene, less than 10,000 years old. About 6 mi of the line.
Metasedimentary, schist. Age: Paleoproterozoic, 1.6 to 1.8 billion years old. About 5 mi of the line.
Gravel, sand. Age: Pleistocene, less than 0.8 million years old. About 3 mi of the line.
Granite, granodiorite, tonalite. Age: Paleoproterozoic, 1.6 to 1.8 billion years old. About 3 mi of the line.
Sand, silt, clay. Age: Pleistocene to Holocene, less than 2 million years old. About 1.0 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 St. Johns reaches the Gulf of California by way of the Gila and the Colorado: about 340 river miles.
210 miles of the trip are on the Gila.
Often dry. About 60% 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 St. Johns; river miles along the main stem, rounded.
St. Johns has a hot desert climate. Summer afternoons average 107° in July; winter nights fall to about 45° in December. About 7 inches of rain fall in a normal year.
On November 14 St. Johns normally reaches 77° and falls to 54°. The record high is 91°, in 1999; the record low 28°, in 1916. The most rain on this date, 1.58 in, fell in 1993.
Normals 1991–2020 and records since 1895 from the Phoenix Area threaded record (Phoenix Airport, 14 miles northeast, 100 ft higher). NOAA, through RCC-ACIS.
