"That's just not running right," she says. "It shouldn't be that high unless something's plugging the grate up ahead."
In her 21 years as a Salt River Project zanjera -- the Spanish word for a woman who tends irrigation canals and ditches -- she's pulled enough surprises out of the Valley's waterways to know better than to predict what this one might be.
"Sometimes we get dead animals up against the grate," she says, driving along and eyeing the ditch. "They fall in and just can't get out. But mostly it's canal moss -- we call it frog moss -- bottles and cans and those plastic milk jugs. And plastic bags and tarps can do a pretty good job of damming it up, too."
At the canal gate, she plunges a rake into the water and pulls up a wet shag of brownish moss and trash that was sucked tight against the grate. The water lets out a loud thwuck as it sluices through the reclaimed opening into the dark hole of a pipe beneath the canal path.
No dead animals this time. But the stinky pile of paper, wood, bottles, cans and disintegrating plastic slopped on the ground holds some unwelcomed tea leaves about the area's future.
"With all the construction going in down here," she says, "we're starting to see more and more pieces of plywood and Sheetrock in these canals. This is really the handwriting on the wall."
With Valley farmland going urban at a rate of about six square miles a year, zanjeros are a dying breed. When alfalfa green gets plowed into stucco brown, much of the water gets diverted to municipal water treatment plants. SRP officials say that about 80 to 90 zanjeros are working today, down from 120 or so in the late 1980s.
Since 1970, the portion of Valley water flowing to urban rather than agricultural uses has jumped from about 35 percent to nearly 80 percent. SRP expects that by 2020 there won't be any large-scale agriculture operations in the Valley.
The practice of moving water hasn't changed much over the past 50 years, says Sid Friar, who started at SRP as a zanjero in 1945 and retired as head of the utility's water operations in 1989. "The idea is to deliver the right amount of water to the right location at the right time."
The job of zanjero is one of the oldest in town. The ancient Hohokams, who built and operated canals from the early days of the first millennium to about A.D. 1450 when their civilization disappeared, probably had their version of zanjeros. Modern zanjeros started when the Valley's canals were first built in the late 1800s.
Delivering water is a hands-on, archaic practice. The zanjeros open and close the small, damlike gates on canals and ditches that allow the water to flow elsewhere.
Down on the farm, those gates direct it to fields. In town, they send it through a neighborhood's network of ditches, pipes and valves -- turning lawns into shimmering ponds.
Like any historical trade, ditch riding, as it's sometimes called, has produced plenty of lore.
Stories abound about farmers taking after zanjeros with pitchforks or shotguns for allegedly shorting deliveries of water. Another tale tells of the zanjero who took water orders while making his own potable deliveries at a local bar. And some urban ditch riders -- often those working for the private irrigation companies hired by residential subdivisions -- have developed close relationships with homeowners who leave them beer or food in back-porch refrigerators in exchange for good service.
But Joyce Thayer is more concerned with the future than the past, and with what will happen to the farms of the southwest Valley.
"They say we're going to have houses for 50,000 people down in Laveen in the next five or 10 years," she says, driving past a real estate sign on Seventh Avenue south of Baseline. "A lot of the older farmers I know have sold off most of their land. But some of the them are trying to stay."
She sees her own job shrinking and her connection to the land disappearing. "When they put all those houses in there, that's thousands of inches of water that I won't be delivering anymore. None of those new subdivisions take flood irrigation. All of them are on their own systems."
Zanjeros may hang on to some jobs in the older urban subdivisions where backyards are still routinely watered by the twist of a neighborhood valve. But newcomers to the old neighborhoods are finding it easier to plug in a sprinkler than to get up in the middle of the night to open their yard's valve.