The Colorado Street Bridge is also called the Arroyo Seco Bridge. It was built in 1913 and is considered one of the world's most beautiful bridges. Before the structure was built, to cross the Arroyo Seco, one would have to descend the steep eastern slope, cross the stream over a smaller bridge, and then climb up the west bank through Eagle Rock Pass. The curves in the bridge were the brainchild of Drake Mercereau as a result of the inablity to find solid footing in the Arroyo Seco creek bed.
In 1989 the structure was declared structurally unfit and the city of Pasadena spent $27.4 million to do a seismic retrofit of its landmark bridge which reopened in 1994.
The bridge stands stands 150 feet high and extends 1,468 feet. It stands parallel to the Pioneer Bridge built in the 1960s for Interstate 210, it was built in mind to compliment the bridge (BTW, if you visit Lower Arroyo Seco Park in Pasadena you can walk under both bridges).