Main Marker - Side A:The Historic Ocean-to-Ocean Highway and Gillespie Dam BridgeIn 1909, Arizona's Territorial Legislature created the Office of the Territorial Engineer to develop a system of roads connecting Arizona's major cities and towns and improve the delivery of the US Mail. The automobile was steadily gaining in popularity and rutted, dirt wagon roads were no longer suitable for this new means of transportation. Shortly after Arizona Statehood in 1912, the State Engineer surveyed a major East-West transportation route across Southern Arizona between the towns of Clifton and Yuma. This early highway route followed the Gila River west from Phoenix, turning south near the small town of Arlington where the Hassayampa River and Gila River meet. The original highway route then turned westerly through the then popular hot spring resort town of Agua Caliente and forded the Gila River near the town of Dome until 1915, when a bridged crossing was constructed further upstream at Antelope Hill. This highway route, however, proved to be unreliable due to frequent washouts during heavy rains and flooding.
The Historic Gillespie Dam Bridge spans the Gila River on Old US 80 Highway, between the communities of Arlington and Gila Bend. Built in 1927 as a Federal Aid Project, the bridge is a unique and elegant reminder of Arizona's rich past and America's transportation history. The bridge is listed on both the Arizona State and National Register of Historic Places and is referred to in the Historic American Engineering Record as a significant technological accomplishment in Twentieth Century engineering design and construction. During the Winter of 2011, the bridge underwent a $7.3 million rehabilitation effort by the Maricopa County Department of Transportation. This project was designated a 2012 Arizona Centennial Legacy Project and included the construction of this interpretive plaza.
In 1921, the highway route was realigned to ford the Gila River just below the newly constructed Gillespie Dam. Heading south toward Gila Bend, the new route was known as the Phoenix-Yuma Highway. The following year, the Arizona Highway Department built a concrete apron on the downstream side of the Gillespie Dam to help automobiles to cross the Gila River. This crossing point also provide to be unreliable, as high water often made passage difficult. Between 1922 and 1926, large trucks, tractors and horse teams were frequently used to pull automobiles across the apron of the dam.
The Arizona Highway Department set about designing an all-weather bridged structure in 1925 to span the Gila River at this location. Construction of the Gillespie Dam Bridge began in February 1926 and later that same year, the American Association of State Highway Officials adopted our present day highway numbering system. When the new Gillespie Dam Bridge opened to traffic on August 1, 1927, it was officially designated part of the early southern continental US 80 Highway.
Lee Moor Construction of El Paso, Texas built the nine-span steel truss bridged crossing of the Gila River for a cost of $320,000. The 1,662-foot-long Gillespie Dam Bridge was unique for its time and one of the longest bridges and the largest steel structure in the state. All of Arizona's major bridges before this were built using reinforced concrete arches which proved to be no match for swollen, flooding rivers. The new design produced a more durable and flexible bridge that could better withstand the force of flood waters.
Bridge design elements include a connected series of rigid through trusses weighing 2.3 million pounds. The bridge has a total of nine steel truss spans - five 200-foot-long trusses centered over the river channel, flanked by two 160-foot-long trusses at each end. Each steel truss features a camelback web configuration with a built-up box beam for the upper and lower steel members. The trusses are supported by solid concrete abutments and pier columns placed on bedrock at a depth of 25 feet, with the deepest pier extending 43 feet below the riverbed.
The new bridge and US 80 Highway through the Arlington Valley became part of the National "Ocean-to-Ocean Highway". Gillespie Dam Bridge carried US 80 transcontinental traffic from 1927 to 1956, when US 80 Highway was shifted east to Rainbow Valley and the Arlington Valley stretch was decommissioned as an interstate route. The operation, care and ownership of the bridge were then transferred from the State of Arizona to Maricopa County.
While the Bridge no longer serves as a segment of the interstate highway system, it is continually used by locals and is enjoyed by travelers who bypass the newer highway to take in a glimpse of an era gone by. Today, historic Gillespie Dam Bridge on Old US 80, nestled between the Buckeye Hills and the Gila Bend Mountains, serves as an integral plan element in the Arizona Department of Transportation's statewide bicycle system plan, the Maricopa County Department of Transportation's Bicycle Transportation Systems Plan and the Maricopa Association of Government's Regional Bikeway Plan.
Gillespie DamThe Gillespie Dam was built in 1921 by Frank Gillespie to supply water to his Paloma Ranch. At the time, it was the largest privately financed concrete irrigation diversion dam in Arizona. The concrete dam was the last of four dams built at this site. The others were made of earth, stone or wood, and were washed out by floods on the Gila River. The current dam was breached in 1993, which was one of the largest dam failures in Arizona history. Another site associated with the construction of the dam and bridge is the Gillespie Dam Construction Camp. The site contains remnants of the of the machinery and structures used to build the dam, including an innovative pulley system for delivering concrete during construction.
Where There is Water, There is LifeFrom its origins in the mountains of Southwestern New Mexico and Southeastern Arizona, the Gila River winds through forests, grasslands and deserts before joining with the Colorado River on its journey to the Sea of Cortez. From prehistory to our present day, the river has never lost its importance to people nor have its life-giving waters lost importance to the many varieties of wildlife that depend on it for survival.
Riparian habitats are a rare commodity in the arid Southwest. in Arizona, these habitats comprise only 1 percent of the land area, yet these narrow, fertile strips along streams and canyon bottoms harbor the greatest diversity of plants and animals of any habitat type - over 600 wildlife species rely on or are associated with these environs.
The term "riparian" stems from Latin, meaning by the river, simply put, it describes an area along or around any body of water. Grasses usually abound here, with a greater variety of shrubs and trees. There may be sedges, cattails, cottonwoods, mesquites and willows, which are tolerant of standing water and saturated soil conditions.
Mallards are one of the most common species of waterfowl in the United States.
You'll also notice a dramatic change in the wildlife. Numerous birds flit among the vegetation. If you check the soft soil near the water, you'll probably find the tracks of raccoons, rabbits and other small mammals.
The many nooks and crannies created by the connected steel members of the Gillespie Dam Bridge are a favorite nesting place of the Cliff Swallow every spring.
Great Blue Herons are common along the Gila River where they hunt for fish and frogs.
Bats roost in riparian trees and feed upon the great number of insects produced here. You may also see tracks of larger animals like mule deer or javelina that visit in search of food and water.
Prior to 1900, 10 percent of Arizona's lands were riparian habitats. Today, less than 1 percent of these valuable habitats remain intact. The degradation and loss can be largely attributed to man's activities. Take away the lifeblood of an ecosystem, and, in time, the ecosystem also dies.
Lowland Leopard Frogs are one of many species of amphibians that rely on riparian areas.
Main Marker - Side C:
Upper PlaqueThis property has been placed on the
of Historic Places
by the United States Department of the Interior
May 5, 1981
Gillespie Dam Bridge was built in 1927 and is historically significant as one of the most important examples of early bridge construction in Arizona.
1926 State of Arizona Maricopa County 1927
Gila River Bridge
Fed. Aid Project 64-B
U.S. Route 80
Arizona Highway Department
Board of Directors of State Institutions
Gov. Geo. W.P. Hunt, Chairman · Vernon Wright, Member · C.M. Zander, Secretary · W.C. LeFebvre, State Engineer · W.W. Lane, Chief Engineer · Geo. B. Shaffer, Dist. Engr.
Board of Supervisors
S.K. Phillips, Chairman · J.T. Bone, Member · C.S. Stewart, Member · R.A. Hoffman, Bridge Engineer · R.V. Leeson, Consulting Engr. · R.C. Perkins, Resident Engr.
Lee Moor Contracting Co. Contractors
Original 1927 Bridge Roller Bearing
Gillespie Dam Bridge Rehabilitation
2012 Arizona Centennial Legacy ProjectIn December 2011, as the historic Gillespie Dam Bridge approached its 85th year of service, the Maricopa County Department of Transportation began a major bridge rehabilitation and repair effort to save one of Arizona's earliest and most significant commerce and transportation treasures.
Bridge rehabilitation activities included the heat straightening of bent steel members damaged over the years by automobiles and large farm vehicles; pipe rail and sway bracing repairs; installation of new approach guard railing; concrete repairs and wing wall modifications; and reinforcement of bridge piers in accordance with United States Department of the Interior and Arizona State Historic Preservation Office guidelines. The repaving of the roadway approaches at each end of the bridge and the construction of an interpretive plaza provide for enhanced public access and enjoyment of this historic structure.
A significant aspect of the rehabilitation project was the span-by-span hydraulic jacking of the bridge to remove the original rused non-functioning roller bearings. New modern pad bearings were installed as part of this effort, which allow for the necessary expansion and contraction of the steel spans during changes in temperature.
Rehabilitation of the Gillespie Dam Bridge has ensured that this historic structure shall be conserved for future generations and allow its enjoyment into Arizona's second century.
Board of Supervisors
Max W. Wilson, Chairman · Andrew Kunasek · Don Stapley · Fulton Brock · Mary Rose Wilcox
County Administrative Officer
David R. Smiith
John B. Hauskins, R.E.2012
Arizona Centennial 1912 - 2012