Page:Popular Science Monthly Volume 88.djvu/84



IGH masonry walled roadways clinging to precipitous mountain sides and so cunningly built that no cement enters into their composition; bridges of solid concrete spanning deep mountain gorges, and tunnels through living rock are only a few of the features of the Columbia Highway, a two hundred mile three million dollar roadway that Oregon is rapidly driving through the heart of the Cascades and Coast Range mountains, down the Columbia River, from The Dalles to the Pacific Ocean.

For two years the work has been underway, guided by engineering experts who first spent months in Europe studying the famous mountain roadways there with the sole object of not duplicating, but of bettering the best the Old World had to offer.

From the Dalles, where it connects with the trunk roads leading into the interior and the East, the highway follows the south bank of the Columbia—second largest river in the United States—and plunges into the rugged and picturesque Cascade Mountains. Here on one side for more than fifty miles is the river, on the other a rock wall rising sheer for heights varying from a few hundred to thousands of feet. It is through this majestic water carved gorge that the engineers faced and solved their hardest problem.

Their instructions were to build a roadway not less than twenty-four feet in width and with a grade not to exceed five percent at any point. A railroad had possession of what little shoring there was along the river, and for this reason the construction force faced miles on miles of cliffs, long reaches of slope deep with slide rock, and a timbered wilderness with earth pitched ready to slip.

The first work called for tunnels and the highway builders were compelled to make several bores through imposing rock points that rushed skyward hundreds of feet as straight as a plumb line. One tunnel at "Storm Point" is more than three hundred feet long. To insure proper light, arches have been cut through on one side to overlook the river at regular intervals.

Here in the mountains has been worked into perfection the ancient art of dry masonry wall construction. There are approximately two miles of the highway built atop such wall work and all along steep mountain sides. In them each stone was cut to fit and to stay for all time where put.

Instead of the usual steel, reinforced concrete was resorted to in building the bridges that span the numerous torrents. One spanning Moffat Creek is the largest flat arch monolithic bridge in America and the largest three-hinged arch in the world. The clear space of the span is one hundred and seventy feet and the arch rises only seventeen-feet in that distance. Another bridge that crosses over a canyon two hundred feet in depth is three hundred and sixty feet long.

One of the biggest problems was encountered in the construction of the highway over slopes where slides threatened. This included work over an immense bed of broken lava rock so restless that it is called "Crawling Mountain." For half a century it alone had prevented a permanent roadway to conect the Inland Empire with western Oregon. The engineers conquered the slides by sinking pillars through the loose super-rock and anchoring to bedrock. On the pillars they built a concrete viaduct just high enough for the slides to thunder harmlessly underneath.

The highest point above the river is attained at Crown Point, a cliff more than seven hundred feet straight up almost from the Columbia.