This Arizona Republic item put me in mind of William Gibson’s early story “The Gernsback Continuum,” a rumination on the golden age of mega-construction. I saw this engineering marvel on a recent drive to Vegas (bookie, debt, showgirl–long story) and it’s an awe-inspiring sight.

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…

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…

Work crews had to build foundations for the arches midway up two sheer cliff faces, hundreds of feet above the river.…

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.

[Nevada side of the Mike O’Callaghan-Pat Tillman Memorial Bridge under construction at the Hoover Dam. Taken May 3, 2009 by squeaks2569]