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| Name | BNSF Mosquito Creek Bridge #8 Chicago, Milwaukee, St. Paul & Pacific Railroad Bridge #Z-1534 |
| Built By | Chicago, Milwaukee, St. Paul & Pacific Railroad |
| Currently Owned By | BNSF Railway |
| Superstructure Contractor | Wisconsin Bridge & Iron Company of North Milwaukee, Wisconsin Unknown |
| Substructure Contractor | Unknown |
| Length | 243 Feet Total, 123 Foot Main Span |
| Width | 1 Track |
| Height Above Ground | 15 Feet (Estimated) |
| Superstructure Design | Warren Pony Truss and Through Plate Girder |
| Substructure Design | Concrete and Steel Pile |
| Date Built | 1911 and 1933 |
| Traffic Count | 1 Train/Day (Estimated) |
| Current Status | In Use |
| Chicago, Milwaukee, St. Paul & Pacific Railroad Bridge Number | Z-1534 |
| BNSF Railway Bridge Number | 463.37 |
| Significance | Moderate Significance |
| Documentation Date | 9/10/2016 |
In 1870, the Sabula, Ackley & Dakota Rail Road (SA&D) constructed a 21-mile railroad line, extending from the Mississippi River at Sabula, Iowa to Preston, Iowa. The following year, an additional 12 miles were completed to Delmar, Iowa. In 1872, an additional 54 miles were completed to Marion, Iowa. In 1872, the SA&D was conveyed to the Milwaukee & St. Paul Railway (M&StP), which reorganized as the Chicago, Milwaukee & St. Paul Railway (Milwaukee Road) in 1874. In 1882, the Milwaukee Road completed an additional 257 miles between Marion and Council Bluffs, Iowa; completing a mainline from the Mississippi River to the Missouri River. The same year, a bridge across the Mississippi River was completed at Sabula, which connected to the existing Milwaukee Road system in Illinois. By the late 19th Century, the Milwaukee Road had developed a large railroad network throughout the Midwest. This line quickly became a principal mainline for the Milwaukee Road, and allowed for the connection and construction of other branch lines throughout Iowa.
In 1901, a short 12-mile cutoff was completed between Green Island, Iowa and Browns Junction, Iowa; which shortened the distance and provided better grades. The original line was retained as a second track. In the early 20th Century, the Milwaukee Road was aware of the importance of this line, and a massive construction project was planned to modernize the line. Between 1912 and 1915, the line between Green Island and Manilla, Iowa was extensively rebuilt, with a second track constructed and large sections of line relocated. The result was one of the most modern double track lines in Iowa, complete with smooth curves, gentle grades and new bridges. After completion of the project, some short sections of the original line were retained as spurs, which were abandoned by the early 1920s. The Milwaukee Road failed to accurately project the level of traffic over this line, and traffic never reached the threshold that required a double track line. The Milwaukee Road was often in financial trouble, especially after the costly Pacific Extension was completed in 1909. In 1925, the company declared bankruptcy, and reorganized as the Chicago, Milwaukee, St. Paul and Pacific Railroad in 1928. Despite the financial strain, this line remained an important mainline for the Milwaukee Road. Segments between Marion and Covington, Iowa; Newhall, Iowa and Collins, Iowa; and Madrid, Iowa and Templeton, Iowa were reduced to a single track in 1934. The segment between Green Island and Paralta, Iowa was reduced to a single track in 1950; the segment between Paralta and Marion in 1954; the segment between Collins and Madrid, Iowa in 1956 and the segment between Covington and Newhall in 1964. In addition, the original line east of Browns Junction was abandoned in 1950. Financial hardship continued through the 20th Century for the Milwaukee Road, and the railroad again filed bankruptcy in 1977. In 1980, the Milwaukee Road decided to abandon the entire Iowa Division mainline. The segment between Bayard, Iowa and Council Bluffs was sold to Burlington Northern Railroad (BN). Segments between Perry, Iowa and Bayard and between Slater, Iowa and Woodward were sold to the Chicago & North Western Railway (C&NW). A short segment at Marion was sold to the Chicago Central & Pacific Railroad (CC).
In 1985, the segment between Herndon and Bayard was abandoned by the C&NW. In 1995, the C&NW was purchased by Union Pacific Railroad (UP). In 1996, BN merged with the Atchison, Topeka & Santa Fe Railway to form BNSF Railway. The CC was purchased by Illinois Central Railroad (IC) in 1996, and the IC was purchased by Canadian National Railway (CN) in 1998. In 1999, the segment between Dawson, Iowa and Herndon was abandoned by UP. In 2002, most of the segment at Marion was abandoned by CN. Between 2003 and 2004, the remaining portions between Slater and Woodward and between Perry and Dawson were abandoned by UP. Today, BNSF operates the Bayard to Council Bluffs segment as the Bayard Subdivision, and CN still operates a short segment of line in Hiawatha. Linn County has developed large sections around Marion into the Grant Wood Trail. A section west of Rhodes, Iowa has been reused as a trail; and segments between Collins and Slater have been reused as the Heart of Iowa Nature Trail. Much of the line between Slater and Perry has been reused as the High Trestle Trail; and the line between Perry and Herndon has been reused as the Raccoon River Valley Trail. Remaining segments have been abandoned, with much of the right-of-way still intact. In addition, large segments of the original right-of-way that was replaced in the early 20th Century remain intact.
Located south of Neola, this pony truss and through plate girder bridge is the eighth crossing of Mosquito Creek along the former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) mainline. The first bridge at this location likely consisted of a timber pile trestle bridge, constructed when the line was first built. In 1899, the bridge was replaced by a 123-foot, 6-panel, pin-connected Pratt pony truss span, set onto concrete abutments and fabricated by the Lassig Bridge & Iron Works. In 1911, the bridge was altered when two through plate girder spans were added to the south end, and new concrete piers and a new south abutment were constructed. In the 1930s and 1940s, the Milwaukee Road invested significant capital into this line, rebuilding and repairing bridges. In 1933, the original truss span was replaced by a heavier span, giving the bridge its present configuration. The truss span was reused at Bridge #T-598 across the Big Sioux River near Hudson, South Dakota. Currently, the bridge consists of a 123-foot, 8-panel, riveted Warren pony truss span, approached by two 60-foot type "C3" through plate girder spans on the south. The abutments and south pier are constructed with concrete, while the north pier consists of a newer steel pile pier.
The truss span follows a standard design for the era, with heavy members, a curved upper angle connection and a standard floor. The top chord and endposts both consist of built-up beams, with X-lacing on the bottom and a solid plate on the top. The bottom chord is composed of a built-up beam which uses X-lacing on both sides. Both the vertical and diagonal members use heavy solid beams, and the vertical members are connected to the floorbeam by a thick triangular plate. The floor consists of two plate girder stringers and plate girder floorbeams, typical for spans from this era. At the upper angle connections, a rounded plate connects the top chord to the endposts. The through girder spans follow a standard design for a type "C3" through plate girder span, with modest sized girders, a standard floor and rounded girder ends at south end of the south span and north end of the north span. Type "C3" girders were a standard Milwaukee Road design, which used four light stringers in the floor system, as opposed to "C4" girders which used two heavier stringers. The south pier has a rectangular shape, while both abutments use sloped wing walls. The north pier consists of steel piles and a concrete cap. An unknown contractor fabricated the girder spans, while Wisconsin Bridge & Iron Company reportedly fabricated the truss span. It is believed that labor employed by the Milwaukee Bridge & Building Department constructed the concrete substructures, although it is unclear if the north pier or repairs were made by railroad company forces or by an unknown contractor. Warren truss spans became popular in the 20th Century, as they were simple, economical and strong. Since the initial construction, the bridge has seen a number of alterations, including the installation of the steel pile pier in the late 20th Century. It is believed this was added due to the failure of the original concrete pier in approximately 1951. Today, the bridge remains in use as part of a BNSF Railway branch line. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked the bridge as being moderately significant, due to the truss design.