Old Trails Bridge
The Old Trails Bridge is several hundred feet south
of Interstate 40 where it crosses the Colorado River at Topock,
AZ. To park and view the bridge, take the Interstate 40 exit for
Park Moabi, the last California exit from the west and the first
from the east. Signs direct visitors to the park. Follow the
Park Moabi Entrance Rd. north to its intersection with the
National Trails Highway/Park Moabi Rd. then turn right.
The first vantage point is from an old brick bridge nearly a
mile from the intersection. Visitors can park on the side of the
road and walk down the bridge top.
The second vantage
point is nearly two miles from the intersection. Visitors should
continue along the National Trails Highway/Park Moabi Rd. past
the first vantage point and intersection with Interstate 40;
then look for a historic concrete billboard and adjacent pullout
pad. This location provides the best view of the bridge.
The steel arch of the Old Trails Bridge simply
soars. An innovative piece of engineering, one enormous span of
600 feet supports the 800-foot bridge that crosses the Colorado
River in Topock, halfway between Yuma and the Utah border. The
bridge carried automobile traffic over the Colorado River from
1916 until 1948.
Builders constructed the Old Trails
Bridge in 1914 partly to compete with the Ocean-to-Ocean Bridge
being built in Yuma, south of Topock. To entice traffic farther
north, the States of Arizona and California and the Bureau of
Indian Affairs decided to erect another substantial span over
the Colorado River. The new bridge would be part of the National
Old Trails Road, an early transcontinental route well underway
to connecting St. Louis to Los Angeles by 1914. In the process,
the designers created a landmark of American civil engineering.
Technologically, the structure is nationally significant as
an outstanding example of steel arch construction. The engineers
for the Old Trails Bridge had studied the problems builders and
engineers encountered while constructing the Ocean-to-Ocean
Bridge. They knew the engineers there had found constructing and
securing a large span over the deep Colorado gorge difficult, so
they tried the task a different way.
In Topock, engineers
used a unique cantilever method of construction assembling
bridge halves on their sides on the ground and hoisting them
into place using a ball-and-socket center hinge. This meant that
the structure was not supported by traditional spans from the
ground up as it was being built. The use of the cantilever was a
daring move for its time, creating the longest arched bridge in
America. At 360 tons, it was the lightest and longest bridge of
its kind. From the day it opened, this graceful arch and the
deck it supported were a pivotal Colorado River crossing, first
on the transcontinental National Old Trails Road and, by 1926,
on Route 66.
The Old Trails Bridge carried traffic for 66
years, until 1947, when cars and trucks began moving onto
interstate systems. In 1948, the deck was removed so the
bridge could accommodate a natural gas pipeline, which it still
carries. The bridge was listed in the National Register of
Historic Places in 1988.