What it means
Granite Reef is where the Salt River stops. Four miles below the point where the Verde joins the Salt, a concrete weir 1,128 feet long and 29 feet high lies across the riverbed, and almost everything that reaches it turns left into the Arizona Canal or right into the South Canal. The river that leaves the dam is, most of the year, a dry channel of sand and tamarisk running past Mesa, Tempe and Phoenix. Locals who know the system say “Granite Reef” for the dam; locals who fish say it for the recreation site beside it on the Bush Highway; the Salt River Project says it for both.
The word matters in Scottsdale because the canal that starts here is the one that runs through Old Town. Every drop in the Arizona Canal, the water under the Soleri Bridge and in the flood-irrigated lawns of Arcadia, came over Granite Reef.
Where you’ll meet it
On the Bush Highway between Mesa and Saguaro Lake, where a brown Forest Service sign marks the recreation site; in SRP water reports; on the Arizona Canal Path, whose water began here; and in the 1900s chapter, when federal reclamation remade the Valley.
Where the word came from
The name was on the site before the dam. “Granite Reef” described a ledge of hard rock across the Salt River bed, the kind of natural sill a canal builder looks for because water can be lifted off it without the structure washing away. The Arizona Canal Company’s 1880s diversion, the Arizona Dam, sat upstream of it, a brush, rock and timber weir that sent water into the canal dug between 1883 and 1885 to open the land north of the river, including the future Scottsdale, to farming.
The Arizona Dam was the weak point of the whole north-side system, and in April 1905 a flood took it out. Farmers under the Arizona Canal were left with a ditch and no river, which is the kind of crisis that gets the federal government involved. The newly formed Reclamation Service, working under the 1902 Reclamation Act and in partnership with the farmers’ own Water Users’ Association, bought the north-side canals and in October 1906 began a permanent concrete diversion dam at the Granite Reef site. It was finished in May 1908, three years before Roosevelt Dam upstream. From then on the engineers’ name for the site became the Valley’s name for the dam, and nobody has ever claimed credit for coining it.
What the dam did was more than replace a weir. By putting both the Arizona Canal headworks and the South Canal headworks on one structure, Granite Reef unified the north and south sides of the Valley into a single system, the one SRP still runs: Roosevelt and the Salt reservoirs above, Bartlett and Horseshoe on the Verde, and one gate at Granite Reef deciding where the water goes. The Arizona water law guide explains the rights that ride on that gate.
What it is not
Granite Reef is not a storage dam. It holds no reservoir and makes no lake; Saguaro Lake, the nearest water people picture, is behind Stewart Mountain Dam ten miles upstream. It is also not the end of the Salt River on a map, only in practice: the channel continues through the Valley to the Gila, and in a big release year, 1993 most famously, the river comes back and runs under the bridges it was always supposed to.
The fine print
The Bureau of Reclamation’s figures: a concrete ogee weir 1,128 feet long, 29 feet high, with 35,000 cubic yards of concrete, a crest elevation of 1,310 feet and a normal operating depth of 18 feet. The north-side headworks are rated at about 2,000 cubic feet per second into the Arizona Canal, the south side at about 1,600 into the South Canal, with sluice gates on each side to flush the sand that a desert river carries. The dam is designed to be overtopped; major releases spill over the crest every 10 to 40 years by design, which is why the Salt River below it occasionally floods and why the 1970 Labor Day flood and the winter of 1993 are remembered.
The water that reaches Granite Reef is already regulated. Nothing arrives there that SRP has not released from Roosevelt, Horse Mesa, Mormon Flat or Stewart Mountain on the Salt, or Horseshoe and Bartlett on the Verde; the dam only divides it. Central Arizona Project water also enters the system through an interconnection near here, so the Arizona Canal carries Colorado River water part of the year, and the Granite Reef Underground Storage Project beside the dam banks surplus water in the aquifer. The Scottsdale Water guide traces how that mix reaches the city’s taps.
The name’s origin is the record’s hole. Reclamation documents use “Granite Reef” from the start of the project without explaining it, and we found no source that identifies who first wrote it down or whether the rock is in fact granite. The Hohokam canal builders took water from this same reach a thousand years earlier; where their headgates stood is also unknown.