A quarter-mile downstream from Hoover Dam, two fingers of concrete stretch toward each other from sheer cliffs, suspended nearly 900 feet above the Colorado River.
In a month, the fingers will meet, an 80-foot gap will close and the longest concrete arch in the Western Hemisphere will be complete.
The union will mark a major milestone in the nine-year construction of the Hoover Dam bypass bridge, scheduled to open in late 2010.
But even incomplete, the overpass, officially known as the Mike O'Callaghan-Pat Tillman Memorial Bridge, evokes a sense of wonder. Towering columns perch on naked rock. The arch is held by tendons of steel cable.
When the four-lane road is laid atop the arch, it will be the third-highest bridge deck in the country.
The bridge is intended to replace the road atop the Depression-era Hoover Dam as the main route between Phoenix and Las Vegas.
The project is designed to speed the trip along U.S. 93 and facilitate more trucking commerce among Canada, Mexico and the U.S.
The $114 million bridge project has been a challenge. Accidents delayed it by two years and claimed one life, as workers battled intense heat, dangerously high winds and perilous heights.
Spanning the Colorado River at Black Canyon is no easy task.
Work crews had to build foundations for the arches midway up two sheer cliff faces, hundreds of feet above the river. Access to the site was only possible by building new roads that will become part of the $240 million bypass.
One worker was killed when a jack used to loosen arch-support cables punctured his chest.
Weather is as big a problem as logistics. Temperatures as high as 120 degrees strain workers and heat up wet concrete. Crews use liquid nitrogen to keep the concrete cool so blocks don't develop fatal cracks.
Wind gusts and lightning strikes also halted work, much of which relies on a high-wire pulley system, including a cable 1,300 feet above the river.
In September 2006, a metal-brace tower holding the Nevada end of the high wire collapsed in 60 mph gusts and fell onto U.S. 93. There were no injuries, but the accident pulled down all of the rigging and the twin tower on the Arizona side, setting back construction two years.
The California joint venture of Obayashi Corp. and PSM Construction USA Inc. had to find temporary replacement parts as far away as Scotland.
The bridge remains on budget, Federal Highway Administration project manager Dave Zanetell said, because crews performed other work during the hiatus.
When the Hoover Dam was finished, it was only accessible to Arizonans via a small dirt road.
That was 1935. Las Vegas was a town of about 8,000 people, and the first casino wouldn't sprout up on the Strip for another decade.
Nobody imagined the traffic that would follow. In 1965, the government began its first study looking into bypassing the dam. It would take 28 more studies and 36 years before the government approved the work in March 2001.
And yet construction would still have to wait because Congress dallied with passing the bill that actually paid for the assembly. "The first bucket of dirt moved on Valentine's Day 2005," said Bonnie Klamerus, deputy project manager for the Federal Highway Administration.
The new bridge is officially named the Mike O'Callaghan-Pat Tillman Memorial Bridge. O'Callaghan was a former Nevada governor and Las Vegas newspaper editor. Tillman was an Arizona Cardinals football star who joined the Army after the Sept. 11 attacks and was killed in Afghanistan.
A long line of cars inches across Hoover Dam, stopping repeatedly for throngs of tourists crossing the road. Anyone who has slogged through this scene knows why the government is building a bypass just downstream.
The new thoroughfare is expected to shorten travel time and reduce the accident rate near the dam, which is triple that of other nearby highways.
In free-flowing traffic, travelers take nearly 17 minutes to traverse the 6 miles from one side of the Colorado River gorge to the other. Cars must navigate hairpin curves, narrow lanes and steep grades.
When the bridge opens, Arizonans wanting to try their luck on the Strip will get there at least 10 minutes faster and drive on a gently curved and mildly sloped four-lane highway.
There are economic benefits too. Arizona officials see U.S. 93 as a third major "NAFTA highway," competing with interstates in California and Texas.
Nogales is the main entry point for Mexican produce in the western United States. State economists want this new route to the Hoover Dam to become a commercial artery to Las Vegas, Salt Lake City and north to Alberta, Canada.
The gap between the two halves of the twin arches has narrowed to 80 feet.
The arches are held in place by a system of cables, looped over temporary towers at each end of the bridge, and anchored under tension.
In August, the final center segment of each arch will be lowered into place.
Then, the cables will be removed one by one, followed by the towers.
The process will take about a month.
Crews will then stack concrete blocks on top of the arch to build the remaining pillars to support the road.
The arches of the Hoover Dam bypass bridge span the canyon behind laborer Romeo Alanik.
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