San Pedro Bridge, Milepost 306.45 on Interstate 10 Business Route, Benson

Source document Quoted word for word from HAER AZ-98. Not written, edited or summarised by this site.

Spanning the San Pedro River at Milepost on Interstate 10 Business Route (I in the City of Benson, in Cochise County, Arizona. The San Pedro Bridge is located at latitude longitude The coordinates represent the structure s center point, and were obtained on January 30, using a Garmin GPSmap accurate to +/ 10 meters. The coordinates datum is North American Datum The San Pedro Bridge location has no restriction on its release to the public.

Source document Quoted word for word from HAER AZ-98. Not written, edited or summarised by this site.

The San Pedro Bridge is an outstanding example of post World War II bridge construction in Arizona and is one of the longest bridges of its type. It is also significant as a key feature of the historically important State Route 86 transportation corridor in southeastern Arizona.

Source document Quoted word for word from HAER AZ-98. Not written, edited or summarised by this site.

A bridge inspection report found the San Pedro Bridge to have serious structural deficiencies. ADOT is planning to remove the existing bridge and build a new bridge over the San Pedro River in The San Pedro Bridge has been determined eligible for listing in the National Register of Historic Places under Criteria A and C. This report was produced on behalf of ADOT to mitigate adverse effects to the property through documentation in accordance with Section 106 of the National Historic Preservation Act and Section of the Department of Transportation Act. Scott Solliday of AZTEC Engineering Group, Inc. wrote the history. Robert G. Graham of Motley Design Group, LLC took the large format photographs. SAN PEDRO BRIDGE HAER No. AZ 98 (Page 2) Part I. Historical Information A. Physical History: 1.

Date of Construction: 2. Engineers: Arizona Highway Department 3. Builder: Fabricated by the Allison Steel Manufacturing Company of Phoenix; Martin Contracting Company of Tucson built the concrete substructure and erected the steel superstructure 4. Original Plans: Original construction and as built plans of subsequent alterations are housed at the History and Archives Division, Arizona State Library, Archives and Public Records, Phoenix. The San Pedro Bridge was Federal Aid Project No. F 5. Alterations: The only significant change that has been made to the San Pedro Bridge since its construction was the replacement of the aluminum guardrails with concrete Jersey barrier guardrails with Thrie beams at the approaches in about (Federal Project No. F 022 3 B.

Historical Context: The San Pedro Bridge at Benson, completed in is significant for its association with post World War II bridge design in Arizona, and with the development of an improved transportation corridor that later became the alignment for Interstate 10. It is located on what was the eastern portion of State Route 86 (SR which was originally designed to provide improved access to communities in southeastern Arizona. This highway alignment quickly became a popular alternate travel route for cross country motorists on U.S. Route 80 (US The simple design of the steel girder superstructure of the bridge crossing the San Pedro River reflects the postwar priorities of the Arizona Highway Department (AHD) to build bridges quickly and efficiently. SAN PEDRO BRIDGE HAER No.

AZ 98 (Page 3) Development of Ranching and Mining in Southeastern Arizona Southeastern Arizona was sparsely populated when the Southern Pacific Railroad was being built, but by the time this southern most transcontinental rail line was completed, silver mining and cattle ranching had quickly expanded throughout the region. Cochise County was created in with the county seat at Tombstone. Two towns, Benson and Willcox, were established along the in they both became important shipping points for the region.1 The Benson railhead primarily served communities to the south.

With limited farming and grazing along the San Pedro River, this small community relied upon transporting ore and goods between the railroad station and the mining town of Tombstone.2 Important rail spurs were soon extended through the area. The New Mexico & Arizona Railway provided service between Benson and Nogales via Fairbank starting in and the Arizona Southeastern Railroad, constructed to Fairbank in connected the mining centers at Tombstone and Bisbee to Benson.3 Willcox, however, quickly became the more important shipping point, primarily due to the volume of cattle that was raised in the area.

The town was in the northern end of the Sulphur Springs Valley, one of the best stock ranges in the West, with thick grass for grazing and an abundant supply of water drawn from shallow wells. By a total of 1.5 million head of cattle were being raised on ranches spread across hundreds of square miles surrounding Willcox.4 Ore from small silver mines at Johnson, Gleeson and Pearce also was shipped from Willcox. 1 Vernon B. Schultz, A History of Willcox, and Environs, Master s thesis, University of Arizona, Tucson, 30 40; Will C. Barnes, Will C. Barnes Arizona Place Names (Tucson: University of Arizona Press, 30, 57. 2 Janet S. Gibson and Janet H.

Strittmatter, Historic Architectural Properties in Benson, Arizona Survey Area, National Register of Historic Places Multiple Property Documentation Form, 3 Henry P. Walker and Don Bufkin, Historical Atlas of Arizona, 2nd edition (Norman: University of Oklahoma Press, 46 47; David F. Myrick, Railroads of Arizona, Vol. 1: The Southern Roads (Berkeley, CA: Howell North Books, 177 4 Schultz, A History of Willcox, 28, 33, 89 Marshall Trimble, Roadside History of Arizona (Missoula, MT: Mountain Press Publishing Company, William S. Collins, Cattle Ranching in Arizona, National Register of Historic Places Multiple Property Documentation Form, State Historic Preservation Office, Phoenix, SAN PEDRO BRIDGE HAER No.

AZ 98 (Page 4) The Benson Stein s Pass Highway In the early twentieth century, transportation planning focused on the development of highways for automobiles. With the designation of a Territorial Road System in the only highway in Cochise County was the Douglas Grand Canyon Highway, a major north south route that traversed the entire length of the Arizona Territory. The southern branch of this road went south from Tucson, and then southeast to cross the San Pedro River at Fairbank, bypassing Benson, and continuing to Tombstone, Bisbee, and the new smelter town of Douglas. This segment of roadway between Tucson and Douglas became part of the Borderland Highway, a designated national route connecting El Paso to Los Angeles.5.

While Benson and Willcox were the primary hubs for rail transportation in Cochise County, only rough wagon roads provided overland access to the two towns. The first wagon road between Benson and Willcox was started in by Dave Adams, a rancher in Texas Canyon, who dragged a mesquite tree to clear a trail. At the beginning of the twentieth century, prolonged drought brought a decline in cattle production around Willcox and the northern part of the county while rising demand for copper turned Bisbee and Douglas into growing boomtowns. Consequently, all county funding for roads went to the southern part of the county.

In individuals from Benson, Cochise, Willcox, Bowie, San Simon, Solomonville, and Safford organized the Northern Cochise County Good Roads Association (NCCGRA) to promote development of public highways. They proposed building a new highway from Lordsburg, New Mexico, to Tucson, which would provide a more direct and shorter route than the existing state highway through Bisbee and Douglas, but those two towns dominated county politics and ignored the concerns of the smaller communities to the north. With no funding available, NCCGRA issued a proclamation asking citizens along the route to contribute two days of their own labor to improving the road.6 However, Willcox and many other communities in northern Cochise County remained isolated.

By this time there was considerable animosity building between the northern and southern parts of the county as communities to the north sought road improvements but politicians in 5 Melissa Keane and J. Simon Bruder, Good Roads Everywhere: A History of Road Building in Arizona, URS Cultural Resource Report 28(AZ), URS Corporation, Phoenix, 61; Mark E. Pry and Fred Andersen, Arizona Transportation History, Report No. FHWA AZ 11 Arizona Department of Transportation Research Center, Phoenix, 24 32. 6 Schultz, A History of Willcox, 205 SAN PEDRO BRIDGE HAER No. AZ 98 (Page 5) the larger southern towns prevented it from happening.

In residents of northern Sulphur Springs Valley filed a petition with the Cochise County Board of Supervisors to create a new county from the northern half.7 The effort was unsuccessful.

The people of Willcox and Bowie consistently voted against county road bonds which never led to improvements in their area and still relied on the cooperation of local residents to keep their roads passable.8 It was not until when floodwaters washed away the small bridge crossing the San Pedro River, that the county took responsibility for maintaining the Benson Willcox Road and building a new bridge.9 The Board of Supervisor s approved only one new highway, planned to extend north from Douglas into the Sulphur Springs Valley, but roadwork progressed very slowly and the northern half remained an unimproved county road for more than ten years.10 The Federal Aid Highway Act of provided federal funding for improvements to seven percent of the highways in a state that comprised its state highway system.

In Arizona designated almost miles as the state highway system, including a new route incorporating Benson.11 The Tucson Benson Bisbee Highway was largely completed by It went from Tucson to Benson, and then south, crossing the San Pedro River at St. David, with improvements to the old state highway through Tombstone, Bisbee and Douglas. In primary highways were designated as numbered routes.

The Tucson Benson Bisbee Highway became part of US 80, incorporating segments of the old Lee, Bankhead, Dixie Overland, and Ocean to Ocean highways across southern Arizona.12 7 Benson Signal, March 10, May 26, 8 Benson Signal, October 6, December 8, 9 Benson Signal, August 16, 23, September 6, Arizona Highway Department 7% System, Arizona Highways, December 10 Benson Signal, April 26, Arizona Highway Department 7% System, Arizona Highways, January Arizona State Engineer, Seventh Biennial Report of the State Engineer to the Governor of the State of Arizona, for the Period July 1, to June 30, (Arizona State Library, Archives and Public Records, Phoenix); AHD, Budget for the Arizona Highway Department, (Arizona State Library, Archives and Public Records, Phoenix).

11 Pry and Andersen, Arizona Transportation History, 36 40. 12 Clayton B. Fraser, Bridges; Arizona Historic Bridge Inventory, National Register of Historic Places Multiple Property Documentation Form, Fraser Design, Loveland, CO, 56 57. SAN PEDRO BRIDGE HAER No. AZ 98 (Page 6) While the southern portion of Cochise County benefited from the construction of US 80, communities to the north still had to contend with poorly graded and unimproved roads. The Cochise County government was particularly opposed to an improved east west road that would link Benson, Dragoon, Cochise, Willcox, Bowie, and San Simon to Stein s Pass at the New Mexico state line.

A Benson Stein s Pass Highway would be much more direct than the meandering route of US 80, and the cut off, would cut the distance from Lordsburg, New Mexico, to Tucson by 60 miles.13 They were afraid that if this route were improved, it would limit the cross country motor tourist business that supported restaurants, hotel, and filling stations in Douglas and Bisbee.

Small incremental improvements were made to the Benson Stein s Pass Highway through the In Dave Adams, supervisor for northern Cochise County, tried to get an appropriation approved for grading the last sixteen miles of roadway from San Simon to the New Mexico state line, but the proposal was voted down by the other two supervisors.14 Northern county residents once again had to rely on their own efforts, and popular subscription from towns along the road paid for the grading. In the Sunset National Highway Association was organized to promote the Sunset Express Route from Los Angeles to New Orleans through southern Arizona, using the shorter cut off. William Coxon, state legislator from Willcox, was president of the Arizona Division of the association.

Coxon introduced a bill in to designate the Benson Stein s Pass Highway a state highway; the bill passed the House but was defeated in the Senate due to opposition by legislators from southern Cochise County. However, even with just grading and minimal improvements, by there was more traffic on the Benson Stein s Pass Highway than on US 80. In northern residents started a new campaign to create their own county from the northern half of Cochise County, which was again unsuccessful.15 Finally, in the Arizona State Highway Commission approved adding the Benson Stein s Pass Highway to the state highway system. It was designated as State Highway 86 (later SR and was allocated for maintenance of the roadway in the budget.

In it was 13 Schultz, A History of Willcox, 205 14 Schultz, A History of Willcox, 206 15 Schultz, A History of Willcox, 207 SAN PEDRO BRIDGE HAER No. AZ 98 (Page 7) added to the federal aid system. Paving of the highway began in and within a year almost all of the highway was completed. The last twenty eight miles, from Cochise to Benson, was paved by Construction of the San Pedro Bridge During World War II fewer people were driving on Arizona highways due to rationing of gasoline and tires, but after the war, the state s population grew rapidly and tourism emerged as a new industry, bringing a considerable increase in automobile traffic on the Arizona State Highway System s miles of primary highways.

The total vehicle miles traveled per year in Arizona climbed from a wartime average of about 1.3 billion to more than 2.6 billion in Many of the bridges in the state were too narrow to accommodate the growing volume of traffic, with larger automobiles traveling at faster speeds. The AHD focused on improving roads and replacing bridges as quickly and economically as possible. This followed national trends at the time, focusing on standard designs for concrete box culverts, concrete slabs, concrete girders, and small steel stringer bridges.18 In early the AHD determined that the three span steel truss bridge crossing the San Pedro River at Benson was one of these obsolete bridges that needed to be replaced and completed plans for Federal Aid Project No.

F The very simple design of the bridge reflected the urgent need to efficiently replace many structures across the state. It had three spans, each consisting of two large girders, supported by concrete abutments and piers, with a concrete bed. The bridge was unadorned, with just a simple beveled pattern on the abutments. On May 20, AHD awarded the contract for the new San Pedro Bridge (Structure No. to the Martin Contracting Company of Tucson. The existing bridge was removed, dismantled, and stored near the construction site and eventually the salvaged steel was transported to the AHD yard in Tucson. The concrete piers and abutments were set on concrete pilings.

The steel superstructure, weighing almost pounds, was fabricated in Phoenix by the Allison Steel 16 Schultz, A History of Willcox, 208 17 Keane and Bruder, Good Roads Everywhere, 26 27, 56, 63; L.I. Hewes, Some Observations on a Modern State Highway System, Papers Presented at the Sixth Arizona Roads & Streets Conference, April 16, 44 52 (Tucson: University of Arizona, AHD, Factual Review, Division of Economics and Statistics, (Hayden Library, Arizona State University, Tempe). 18 Fraser, Bridges; Arizona Historic Bridge Inventory, 85 92. SAN PEDRO BRIDGE HAER No. AZ 98 (Page 8) Manufacturing Company.

The bridge was completed in at a total cost of By an estimated vehicles per day passed over it.20 The San Pedro Bridge has a total length of 402 and a width of 35 , with a clear roadway of 30 . Since its completion, the only significant alteration of the structure was the replacement of the aluminum guardrails with concrete Jersey barrier guardrails. It is significant for its simple and economical design, and its considerable length.21 When Interstate 10 (I 10) was being built through Cochise County in the the most direct route, via Benson, Willcox, and Bowie, slightly north of the SR alignment was selected for the new highway.

A small portion of the old SR 86 highway on the east side of Benson was designated Business Route 10 (I the historic San Pedro Bridge is located on this portion.22 19 Fraser, Bridges; Arizona Historic Bridge Inventory, 264 AHD, San Pedro Bridge As Built Plans, Federal Aid Project No.

F (ADOT, Phoenix); AHD, Log of the Arizona Highway System Division of Economics and Statistics, (Hayden Library, Arizona State University, Tempe); Arizona State Highway Commission, Construction and Rights of Way Estimates for the Arizona Highway Department for 51, (Arizona State Library, Archives and Public Records, Phoenix), 20 Schultz, A History of Willcox, 209 21 Fraser, Bridges; Arizona Historic Bridge Inventory, 264 22 Pry and Andersen, Arizona Transportation History, 58 61, 75; AHD, San Pedro Bridge As Built Plans, Federal Aid Project No. F SAN PEDRO BRIDGE HAER No. AZ 98 (Page 9) Part II. Structural/Design Information A. General Statement: 1. Character: The San Pedro Bridge is a three span steel cantilever plate deck girder bridge.

The simple design of the steel girder superstructure of the bridge crossing the San Pedro River reflects the urgent need in the mid twentieth century to replace inadequate bridges in Arizona with larger bridges that could be built quickly and efficiently. With a total span of 402 , it is one of the longest bridges in the state. 2. Condition of fabric: A bridge inspection report found the San Pedro Bridge to have serious structural deficiencies.23 The bridge is supported by a two girder superstructure, which is fracture critical; failure of one girder would result in the collapse of the entire bridge. The bridge deck is in poor condition with numerous transverse cracks, severe scaling, spalling, and exposed reinforcing iron. Corrosion has been noted along the bridge spans and girders.

Moreover, the pier foundations are scour critical, and the bridge approaches have deteriorated. The bridge cannot be repaired and brought up to current highway design standards without loss of integrity of design, material, and workmanship; therefore, it will be replaced with a new bridge. B. Description: The San Pedro Bridge has a total length of 402 0 , including abutments, and a width of 35 0 , with a clear roadway width of 30 0 . Its primary components include a concrete substructure supporting a steel cantilever plate deck girder superstructure.24 The bridge's substructure consists of reinforced concrete abutments, wingwalls, and piers over concrete piles.

The two abutments are stub abutments supported by one row of 16 diameter concrete piles, featuring subtle, decorative chamfered patterns on the side walls. Each of the two piers consist of two tapered columns connected by a pier wall. The columns are 5 6 in 23 Kimley Horn and Associates, Inc., Final Project Assessment, San Pedro River Bridge, Existing Structure No. 350 (Prepared for the ADOT, Project Nos. B10 CH 306 B10 Benson Stein s Pass Highway, I MP 24 Kimley Horn, Final Project Assessment; Fraser, Bridges; Arizona Historic Bridge Inventory, 264 Arizona Highway Department, San Pedro Bridge As Built Plans, Federal Aid Project No. F SAN PEDRO BRIDGE HAER No. AZ 98 (Page 10) diameter at the base and 4 0 in diameter at the top. The steel girders bear on the top of the columns.

Each pier is supported on a concrete pile cap and 36 16 diameter concrete piles. Each pier and each abutment have two fixed shoe bearings.25 The superstructure is comprised of three long steel girder spans a 160 0 center span flanked by 105 0 approach spans on both ends. Each span was made up of two deep deck girders with riveted angle flanges and web stiffeners spaced 5 0 apart. The central span cantilevers over the piers, tapering slightly in height from 8 4 to 6 6 to match the smaller height of the approach spans. This increased the span length and reduced the number of cast steel bearing shoes at each pier to two. The girders have flanges that extend beyond the ends with riveted connections to join the approach span girders with the center span girders.

Transverse floor beams are 5 0 girders with riveted web stiffeners, which support 4 steel stringers. Steel angle lateral braces tie into the deck girders at the bottom of each floor beam. The deck girders carry a reinforced concrete deck that is 30 0 wide and 6 thick with an overhang length of 3 9 . Both sides of the deck are bound by concrete Jersey barrier guardrails with Thrie beams at the approaches.26 A pair of timber revetment walls near the west abutment are remnants from the earlier steel truss bridge that was located at the site. C. Site Information: The San Pedro Bridge is located in the San Pedro Valley at an approximate elevation of above mean sea level (amsl).

It spans the San Pedro River, a perennial river that flows north through a broad floodplain bound by gently sloping hills. The bridge spans the river about 35 above the riverbed. The riparian habitat within the floodplain of the San Pedro River includes salt cedar intermixed with sparsely scattered Fremont s cottonwood and Goodding s willow. Other vegetation includes mesquite, Johnson grass, green bristlegrass, desertbroom, and other grasses and herbaceous forbs. 25 Ibid. 26 Ibid. SAN PEDRO BRIDGE HAER No. AZ 98 (Page 11) Part III.

Sources of Information Archival research was conducted at the following repositories: Arizona State Library, Archives and Public Records, Phoenix Arizona Department of Transportation, Phoenix Arizona Historical Society, Tempe Hayden Library, Arizona State University, Tempe The key sources for compiling the written historical information are records of the AHD and technical reports prepared for ADOT over the past ten years. The available contextual information on the San Pedro Bridge is found to be reliable and accurate. Research was thorough, and no additional sources of information have been identified. A. Primary Sources Arizona Highway Department. Budget for the Arizona Highway Department, Arizona State Library, Archives and Public Records, Phoenix. Factual Review.

Division of Economics and Statistics, Hayden Library, Arizona State University, Tempe. Log of the Arizona Highway System Division of Economics and Statistics, Hayden Library, Arizona State University, Tempe. San Pedro Bridge As Built Plans, Federal Aid Project No. F Arizona Department of Transportation, Phoenix. Arizona Highways, Arizona State Engineer. Seventh Biennial Report of the State Engineer to the Governor of the State of Arizona, for the Period July 1, to June 30, Arizona State Library, Archives and Public Records, Phoenix. Arizona State Highway Commission. Construction and Rights of Way Estimates for the Arizona Highway Department for 51. Arizona State Library, Archives and Public Records, Phoenix. SAN PEDRO BRIDGE HAER No. AZ 98 (Page 12) Benson Signal, Hewes, L.I.

Some Observations on a Modern State Highway System. Papers Presented at the Sixth Arizona Roads & Streets Conference, April 16, 44 52. Tucson: University of Arizona, Kimley Horn and Associates, Inc. Final Project Assessment, San Pedro River Bridge, Existing Structure No. Prepared for the Arizona Department of Transportation. Project Nos. B10 CH 306 01C and B10 Benson Stein s Pass Highway, I MP B. Secondary Sources Arizona Highway Department. History of the Arizona State Highway Department. Highway Planning Survey, Phoenix, Barnes, Will C. Will C. Barnes Arizona Place Names. Edited by H. Granger. Tucson: University of Arizona Press, Collins, William S. Cattle Ranching in Arizona, National Register of Historic Places Multiple Property Documentation Form.

State Historic Preservation Office, Phoenix, Fraser, Clayton B. Bridges; Arizona Historic Bridge Inventory. National Register of Historic Places Multiple Property Documentation Form. Fraser Design, Loveland, CO, Benson Bridge, Cochise County, Arizona; Statement of Significance. Fraser Design, Loveland, CO, Gibson, Janet S. and Janet H. Strittmatter. Historic Architectural Properties in Benson, Arizona Survey Area. National Register of Historic Places Multiple Property Documentation Form, Keane, Melissa, and J. Simon Bruder. Good Roads Everywhere: A History of Road Building in Arizona. URS Cultural Resource Report 28(AZ), URS Corporation, Phoenix, SAN PEDRO BRIDGE HAER No. AZ 98 (Page 13) Myrick, David F. Railroads of Arizona, Vol. 1: The Southern Roads.

Berkeley, CA: Howell North Books, Mark E., and Fred Andersen. Arizona Transportation History. Report No. FHWA AZ 11 Arizona Department of Transportation Research Center, Phoenix, Schultz, Vernon B. A History of Willcox, and Environs. Master s thesis, University of Arizona, Tucson, Trimble, Marshall Roadside History of Arizona. Missoula, MT: Mountain Press Publishing Company, Walker, Henry P. and Don Bufkin Historical Atlas of Arizona. 2nd ed. Norman: University of Oklahoma Press, SAN PEDRO BRIDGE HAER No. AZ 98 (Page 14) San Pedro Bridge Figure 1. Location Map SAN PEDRO BRIDGE HAER No. AZ 98 (Page 15) Figure 2. Vicinity Map SAN PEDRO BRIDGE HAER No. AZ 98 (Page 16) San Pedro Bridge Figure 3. Detail from Cochise County General Highway and Transportation Map, prepared by the AHD,