Depending on your point of view, the new Skywalk jutting out over the south-western rim of the Grand Canyon is either an irresistible attraction giving visitors a whole new perspective on the breathtaking scenery below, or an abomination that threatens to turn one of the great natural wonders of the world into Disneyland self-parody.
Either way, the latest project to draw visitors to Arizona's signature attraction is certainly generating a lot of publicity. On Wednesday, the 70ft-wide horseshoe-shaped platform was slotted into place, 4,000 feet above the canyon floor, before a large audience of news reporters, property developers and members of the local Hualapai tribe. The Hualapai blew into gourds, burned sage and gathered around a spiritual leader called Emmett Bender, who blessed the new structure even as he called it "the white man's idea".
For the next 12 days, the engineers will complete their welding and harnessing work - nobody wants any slippage, or a repeat of the wobble problems that plagued the Millennium Bridge in London - after which no less a figure than Buzz Aldrin, the second man to set foot on the moon, will make a ceremonial first circuit of the horseshoe. Then, on 28 March, the Skywalk will open to the public.
Shuttle buses will ferry visitors over the last 14 miles of unpaved road where, for the giddy price of $74.95 (£39) - $49.95 for a basic Hualapai reservation visiting package and another $25 for the Skywalk itself - they will be invited to don special non-scratch booties over their shoes and step on to the glass walkway to simulate a sensation of floating over the abyss. The edge of the glass walkway will be opaque to reassure the faint of heart, while the middle will be entirely transparent.
It's quite some feat of engineering. Weighing more than a million pounds, it is as heavy as four Boeing 757 jets. That requires some considerable harnessing to the canyon wall - indeed, the first contractor to start building the Skywalk was so unnerved by the possibility of failure that it walked off the job last October.
Rolling the Skywalk into place required a complex set of hydraulic "shoes" that lifted the structure above a cement track and rolled it across a bed of metal rods to a set of four steel anchors attached firmly to the canyon rock. To stop it tipping over before it could be secured, engineers loaded the back end with half a million pounds of steel cubes as a counterweight.
More striking than the engineering work, though, is the commercial bargain that has been struck to make the Skywalk a reality. The Hualapai have languished in poverty ever since cross-country traffic stopped using the mythical old Route 66, which runs through their main settlement, Peach Springs, and opted instead for the interstate highway constructed in 1979, some 30 miles to the south.
Some hardier visitors still pass through to admire the Grand Canyon from its western end - about 250,000 last year, according to local estimates - but their numbers pale in comparison with the four million who visited the Grand Canyon National Park's southern rim, 250 miles further east.
It's not that the canyon is any less beautiful at its western end. It's a question, rather, of amenities. The Hualapai can't offer paved roads, or hotels, or restaurants, or visitor centres, or even a supply of running water. The western end is out of the question for the big tour buses that roll up to the southern rim from Flagstaff every day, and it goes unpublicised by the national parks service, whose Grand Canyon park does not extend this far west.
For the past decade or so, Hualapai leaders have been trying to dream up ways to enrich themselves. First they tried developing casinos - a tactic that has worked spectacularly for other native Americans, especially in California, where a special compact with the state government was signed nine years ago, generating billions of dollars in tax-exempted revenues. The Hualapai casinos were a failure, however, in part because of their remote location, and also because Peach Springs is a mere 120 miles from Las Vegas, the biggest casinoon the planet.
It was Las Vegas, though, that gave rise to an altogether smarter plan: offering tourists to Sin City an easy daytrip to a Grand Canyon landmark - just two hours' drive instead of four, or five out to the National Park. A Las Vegas developer called David Jin first dreamed up the Skywalk a decade ago and finally agreed to bankroll it out of his own pocket, to the tune of $30m. The Hualapai leaders agreed to his plan, on condition that they would take ownership of the Skywalk and any subsequent developments, and keep the lion's share of the profits.
The business plan is detailed and, in its way, quite relentless. The aim is to double the number of visitors to the Hualapai reservation in the first year. Revenue from the Skywalk will then be pumped into full-scale tourist development - a visitor centre, museum, cinema, gift shop and several restaurants. The helicopter landing pad at Grand Canyon West will be expanded to accommodate larger aircraft.
This is a project with Las Vegas stamped all over it. The investor is from Vegas, the construction company is from Vegas, and all the engineers and builders are from Vegas too. The fear is that the Grand Canyon itself will come to be seen as just another Vegas attraction - a place where tourists can come, be amazed, and lose as much of the contents of their wallets as can be prised out of them.
Environmental purists see the Skywalk as an unacceptable desecration of the Grand Canyon's natural beauty. Some Hualapai tribe members worry that material greed will supplant more fundamental, spiritual values. The Skywalk and its associated projects sit on land where Hualapai ancestors are buried. Perhaps even more profoundly, Hualapai tradition has it that this corner of the south-western American desert is the origin of human life itself. Is that an appropriate site for a gimmicky tourist attraction?
Robert Arnberger, a superintendent of the Grand Canyon National Park, calls it a "travesty". "I understand the need for the tribe to consider the economics of the tribe," he told the Washington Post, "but... it desecrates the very place the Hualapai hold so dear."
According to some disgruntled members of the tribe, the Hualapai's ruling council voted to approve the project without fully consulting the community first. "Our ancestors roamed this land before us. This is holy ground," tribe member Leatrice Walema complained a few weeks ago. "Most of our elders disapprove of this, but... it was hidden from us. David Jin is trying to control everything. This should never have been done."
The counterargument is strictly pragmatic - the Hualapai need to eat, and educate their children, and improve their dilapidated houses, and the Grand Canyon is the only resource they have - the only resource they have ever had. Charlie Vaughn, the tribal chairman, dismissed his critics at the opening as people who are "eating tofu and pilaf and sitting in Phoenix with their plasma-screen TVs". "Our tribe started in these canyons," he said. "We've always been here, and we'll always be here."
Even tribal members who agree with him clearly harbour mixed feelings. Emmett Bender, the elder who performed the blessing ceremony, likened the Skywalk to other innovations from the white man, like cars and buses. "We've got to give it a chance," he said with less than total enthusiasm.
Even before the Skywalk, the Hualapai did their best to squeeze maximum advantage from their lands at the Grand Canyon's edge.
Because they have full ownership of their own land, they are not subject to the same restrictions as the national park, which belongs to the federal government. Helicopters are permitted to swoop deeper into the canyon here and boats and rafts are allowed to course along the Colorado River in the canyon basin with greater frequency.
Had the Skywalk been built on state or federally owned land it would have been subject to exhaustive environmental impact reviews, water assessments and a whole bunch more red tape besides. As it was, David Jin and his partners merely needed to win over the Hualapai council.
That leaves a lot of unanswered questions about roads, about water and waste management, about future power sources - for the moment, Peach Springs and Grand Canyon West run on generators - and a host of other issues. For now, trucks bring in food and water and ferry waste directly out. If visitor numbers start edging towards the millions though, that system is rapidly going to become untenable.
Any development in a place like the Grand Canyon is bound to be controversial, of course. The much-visited southern rim of the national park is hardly a thing of beauty either - a cluster of overpriced motels, coach car parks and family restaurants whose only real virtue is to concentrate the tourist eyesores in one relatively contained geographical area.
Fans of the Skywalk argue that it is at least an admirable structure, offering fine if not also unique views (though the views of the canyon are said to be better from nearby Guano Point). And there is one more lure that may or may not attract the requisite attention in the near future: it is surely the perfect location for a James Bond movie action sequence. Never mind the Grand Canyon: is 007 ready for his close-up?
* The canyon is 277 miles long, and from 400 metres to 18 miles wide.
* The bed of the Colorado River is 1,800 metres below the highest point of the rim.
* The canyon attracts five million visitors a year.
* In summer, the temperature difference between the canyon floor and the rim can be as much as 16C.
* Since the 1870s, there have been more than 600 deaths at the Grand Canyon, including 50 falls, 47 suicides, and 128 killed in a plane crash.
* The Grand Canyon National Park was created in 1919. It is now a Unesco world heritage site.