The Blackwater 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.
Blackwater’s center stands about 1,380 ft above sea level. Within three miles the land runs from 1,330 ft to 1,420 ft, a difference of 90 ft: gently rolling country. The highest named summit within 15 miles is Santan Mountain, about 3,020 ft, 12 miles northwest.
Under the town center the state geologic map shows Quaternary surficial deposits, undivided (sand, silt, clay), from the Pleistocene to Holocene, less than 2 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 18×. 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 10 mi of the line.
Silt, clay. Age: Holocene, less than 10,000 years old. About 9 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.
Sand, gravel. Age: Holocene, less than 10,000 years old. About 2 mi of the line.
Granite. Age: Mesoproterozoic, 1.4 to 1.4 billion 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.
A raindrop that lands in Blackwater reaches the Gulf of California by way of the Little Gila, the Gila and the Colorado: about 390 river miles.
260 miles of the trip are on the Gila.
Often dry. About 70% 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 Blackwater; river miles along the main stem, rounded.
Blackwater 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 Blackwater 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, 4 miles southeast. NOAA, through RCC-ACIS.
