The St. David 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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88° on Nov. 11, 1973, the hottest reading for this week of the year since 1923. Next is 87° in 1999.
St. David’s center stands about 3,630 ft above sea level. Within three miles the land runs from 3,590 ft to 3,990 ft, a difference of 400 ft: hilly country. The highest named summit within 15 miles is Apache Peak, about 7,630 ft, 13 miles west-southwest.
Under the town center the state geologic map shows Holocene river alluvium (sand, gravel), from the Holocene, less than 10,000 years old.
The section below crosses 8 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.
Sand, silt, clay. Age: Pleistocene to Holocene, less than 2 million years old. About 9 mi of the line.
Conglomerate, sandstone. Age: Early Miocene to Pleistocene, 2 to 16 million years old. About 8 mi of the line.
Sandstone, shale, limestone. Age: Early Cambrian to Late Mississippian, 330 to 540 million years old. About 2 mi of the line.
Sand, gravel. Age: Holocene, less than 10,000 years old. About 2 mi of the line.
Limestone, dolostone, quartzite. Age: Neoproterozoic to Early Triassic, 248 to 544 million years old. About 1 mi of the line.
Metasedimentary, metavolcanic, gneiss. Age: Paleoproterozoic, 1.6 to 1.8 billion years old. About 0.8 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 smaller units along the line are not listed.
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. David reaches the Gulf of California by way of the San Pedro, the Gila and the Colorado: about 560 river miles.
330 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. David; river miles along the main stem, rounded.
St. David has a cold semi-arid climate. Summer afternoons average 99° in June; winter nights fall to about 27° in January. About 12 inches of rain fall in a normal year.
On November 14 St. David normally reaches 74° and falls to 34°. The record high is 85°, in 2025; the record low 24°, in 2022. The most rain on this date, 0.37 in, fell in 2011.
Normals 1991–2020 and records since 1923 at Benson 6 SE, here. NOAA, through RCC-ACIS.
