The San Tan Valley 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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96° on Nov. 13, 1999, the hottest reading for this week of the year since 1906. Next is 94° in 1953.
San Tan Valley’s center stands about 1,520 ft above sea level. Within three miles the land runs from 1,470 ft to 1,580 ft, a difference of 110 ft: gently rolling country. The highest named summit within 15 miles is Santan Mountain, about 3,020 ft, 11 miles west.
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 32×. 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 10 mi of the line.
Gravel, sand. Age: Pleistocene, less than 0.8 million years old. About 7 mi of the line.
Granite. Age: Mesoproterozoic, 1.4 to 1.4 billion years old. About 3 mi of the line.
Metasedimentary, schist. Age: Paleoproterozoic, 1.6 to 1.8 billion years old. About 2 mi of the line.
Sand, gravel. Age: Holocene, less than 10,000 years old. About 2 mi of the line.
Gravel, sand. Age: Late Pliocene to Pleistocene, 0.8 to 3 million 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.
San Tan Valley has a hot desert climate. Summer afternoons average 107° in July; winter nights fall to about 36° in December. About 8 inches of rain fall in a normal year.
On November 14 San Tan Valley normally reaches 79° and falls to 44°. The record high is 93°, in 1999; the record low 27°, in 1993. The most rain on this date, 1.36 in, fell in 1968.
Normals 1991–2020 and records since 1906 at Casa Grande Natl Monument, 14 miles south, 100 ft lower. NOAA, through RCC-ACIS.
