Pasadena's Colorado Street Bridge, which turns 100 this December 13, bears more than a passing resemblance to an ancient Roman aqueduct. In a way, that makes sense. Both use the same engineering solution – colossal arches – to create an artificial topography and overcome the natural contours of the land.
In Pasadena's case, those contours are the consequence of the Arroyo Seco, a seasonal watercourse that flows through a deep ravine from the base of the San Gabriel Mountains to its confluence with the Los Angeles River. Pasadena's historic core sits atop an elevated mesa that, to the west, drops suddenly into the arroyo. To get from Pasadena to Highland Park, Garvanza, and other westward settlements, travelers faced two obstacles: the stream of the Arroyo Seco itself, and its ravine.
The earliest bridge in the area – J.W. Scoville's wooden trestle span, built in the late 1880s – overcame only the first obstacle. Travelers still had to descend into the ravine, cross the bridge, and then climb the opposite bank – a true hardship for horse-drawn vehicles, but an almost insurmountable one for the early automobiles that began using the bridge around the turn of the 20th century. So when Pasadena resolved to build a new bridge that would extend Colorado Street over the Arroyo Seco, it commissioned a structure that would cross the ravine at street level.
Based on a design by engineer Joseph Alexander Low Waddell with modifications by builder John Drake Mercereau, the Colorado Street Bridge spans 1,467½ feet with the aid of 11 arches. At its tallest, the reinforced-concrete structure soars nearly 150 feet above the streambed.
Upon its completion it was hailed as the longest and tallest bridge in Southern California. But what makes the structure's scale even more impressive are two charming quirks: a 52-degree curve in the bridge's center, and a constant 2.65 percent grade – a result of the fact that the east bank is 30 feet higher than the west.
Construction began in July 1912 and lasted 18 months, employing 40 to 100 workers on any given day. Built with 11,000 cubic yards of concrete – made from gravel collected from the arroyo – and 600 tons of steel reinforcement, the bridge cost a total of $235,000.
In later years, the bridge carried the fabled Route 66 over the arroyo and transformed Colorado Street into Pasadena's main commercial corridor. To accommodate the increased auto traffic, the city widened Colorado by 28 feet between 1929 and 1930, slicing off the facades of old buildings. In 1958, it promoted Colorado Street to the status of boulevard.
But such change was still decades off when, on December 13, 1913, Pasadena residents climbed into their automobiles – specially decorated for the occasion – and paraded across the span, celebrating the creation of their city's most enduring visual landmark.