For weary workers, it's simply called "the pile."
They've been at their task, to sort through and remove, piece by piece, this Everest of twisted steel and dull-gray debris, for more than a week now.
But as hope for finding survivors fades, the cleanup is presenting a logistical challenge as complex as - if not more than - the construction of the World Trade Center 30 years ago.
Cities have been pummeled before, by earthquakes or bombs, and large buildings have come smashing to the ground - many rescue workers here know this well. But never has there been a catastrophe so immense, in so small a space. Before its collapse within these few blocks of lower Manhattan, the two 110-story skyscrapers teemed each day with enough workers and visitors to fill a city the size of Santa Clara, Calif.
"This is different from anything anybody's ever addressed," says Beau Hanna, a debris subject matter expert with the Army Corps of Engineers. "There's more variables in this than we've probably had in any other mission.... The volume, the problem getting to it - it is unprecedented."
Brigades of engineers, ironworkers, and other construction workers have joined the rescue teams and law-enforcement officials to remove what is now estimated to be 1.2 million tons of debris. This pile covers 12 to 15 city blocks where the World Trade Center complex once stood - though investigators say most of the debris is smashed into the six stories of shops, parking lots, and train stations that were beneath the surface.
At ground zero, where dust still hovers like an eerie fog, the cleanup plans are not sketched in blueprints, and hidden dangers often lurk just beneath the rubble, riddled with chasms and voids.
"When I was out on the pile, I was blown away at the treacherous conditions," says Jim Chesnutt, a worker with the Federal Emergency Management Agency (FEMA). "I'm amazed more people don't get hurt in the recovery process."
The removal, thus, is slow and complex. Some workers have just scooped debris with their hands, filling five-gallon buckets and passing them down the pile, one by one, to an investigator.
The ironworkers lug in air machines for their blowtorches and slings and shackles for their mammoth cranes. At the direction of a city engineer, they cut through giant beams, lift them out, and swing them over to a flatbed truck. Or, they just cut through mangled steel until they find a void.
"The head mucketymuck of the fire department down there, he picks and chooses where we cut," says Norman Finnegan, a New York ironworker. "And when he says stop, we stop, so they can get in there with the dogs."
Most times, a rescue team bringing in the dogs is one of the 10 Urban Search and Rescue units sent in by FEMA. Each unit, composed of 62 specialists in various fields, surveys uncovered voids and plans a course of action.
Sometimes the teams tunnel deep beneath the debris. Randy Gross, a canine specialist with California Task Force 7, was with team members in a void near the subway turnstile, in the fourth-floor basement under Tower 1. When he and his dog Dusty came upon a flat black surface, he thought is was just asphalt, so he sent the dog in. It turned out to be a deep pool of oil from crushed cars in the garage above, and Dusty had to be pulled to safety.
Yet even as workers toiled in both the bowels and the surface of what was once the World Trade Center, the Army Corps of Engineers was working with city officials to finalize a master debris-management plan. That will outline, among other things, how the debris should be sorted, separated, and possibly recycled.
Right now, more than 50,000 tons of debris have been brought to a landfill in Staten Island, an outer borough of New York City. There, too, investigators comb through the wreckage. But for many engineers working at the site, the real challenges are still to come.
In the center's six lower levels, crushed cars leak gas and oil. There are also wet-acid batteries, as well as Freon from air conditioners and blood from a blood bank in the center.
These hazardous conditions are complicated further by the "slurry wall," the barrier put up during the construction of the center's foundation, to hold back the earth, muck, and water that would ooze into the six-story hole. The slurry wall was breached during the collapse, engineers believe, and removing the debris could cause another collapse of muddy earth, which would cover everything in the hole.
"As they remove the debris, they'll have to reinforce the slurry wall," says Mr. Hanna. "And you can't just bring in front-loaders and scoop stuff up. You'll have to be pulling things up with cranes and long reach, and that makes things much more difficult."
Even as determined workers put in long hours, however, the difficulties of their task begin to weigh on them.
"You can only look at so much," says Mr. Finnegan, his spent voice dropping to a mumble. "Then you have to walk away, take a break, go down by the river. You can see it: The guys are working [so hard] down there, but you see it in their eyes - they're ready to cry."