The Globe-Show Low Highway: An Engineering Triumph

The very first road in Arizona was established in 1846 by Capt. Philip St. George Cooke as he led the soldiers of the Mormon Battalion across southern Arizona. It was during the Mexican-American War, and the battalion had been tasked with creating a wagon road between Santa Fe and San Diego for Army use. The road—really just a track in its early days—came to be known as Cooke’s Wagon Road.

By 1927, Arizona had a state highway system with just over 2,000 miles of roads crisscrossing the state. In 1926, out-of-state drivers logged more than 250 million vehicle miles on the state’s roadways. Some of Arizona’s highways regularly carried 5,000 cars per day, despite the fact that only ten percent of the state’s road miles were paved.

By this time, major highways connected Globe to Phoenix, Tucson, Safford, and Show Low. But reaching Show Low meant circling to the south to San Carlos and then through Fort Apache and McNary. 

The formidable Salt River Canyon stood in the way: a 2,200-foot-deep gorge that served as the boundary between the White Mountain Apache lands to the north and the San Carlos Reservation to the south. 

Today known as the “mini Grand Canyon,” in 1908 the Arizona Silver Belt called the Salt River Canyon “one of the roughest pieces of country on earth” – but also “some of the grandest scenery on the continent.”

The construction of a road across the Salt River Valley finally began in 1931. Depression-era Federal highway dollars, plus developments in engineering and construction, made the project possible – and the need for an all-weather route to the north made it necessary.

The stretch of highway crossing the Salt River Canyon was one of the first roads in the country to be built with modern heavy construction equipment and techniques, including bulldozers, portable drills, blasting, and massive cuts and fills to master the extremely tough terrain. The highway hugs the cliffs, forcing drivers to negotiate hairpin turns as the road switchbacks down to the river and up the other side of the canyon.

The William A Sullivan Bridge across the Salt—the project’s centerpiece—was built in 1934, with a design by architect Lee Moor and funding from the Public Works Administration. The construction involved many engineering challenges. Due to a shortage of concrete, the bridge had to be designed as a single free span over the canyon, resulting in its two-hinged steel deck arch design.

The bridge was the first that the state Highway Department built with a girder-ribbed steel arch. Thanks to its design, the bridge also could be built more quickly than the usual spandrel-braced arch, so the new technique soon became standard.

When complete, the bridge awed observers with its grace, thanks in part to the decorative steel pylons at the arch corners and the ornamented guardrails along the curving concrete deck.

The Salt River Canyon bridge is a landmark of design and technology, appearing on the National Register of Historic Places. Although the original bridge has been replaced by a modern, wider one, it’s still possible to cross the old bridge, as it now carries a footpath.

The Globe-Show Low Highway was completed in 1938 and is still an example of outstanding road engineering.