Located roughly six miles from Hanover, not far off of Centennial Road, is a small bridge easily driven over without noticing its beautiful structure and historical significance. John’s Burnt Mill Bridge, sometimes referred to locally as Camelback Bridge, was accepted into the list of National Register of Historic Places in 1974. (Its official designation for the county is Bridge No. 56.) It spans the south branch of the Conewago Creek in Mount Pleasant and Oxford Townships, Pennsylvania.
While there are some discrepancies regarding the construction date of the bridge, ranging from 1800 through 1824, the nomination form lists the range of 1800-1823. A plaque on the bridge marking its rehabilitation in 2005-2006 noted the original construction date as 1820.
The roughly 75 foot long bridge has a main section approximately 50 feet in length with approaches (at the time of the nomination) twelve feet each in length, with walls four and a half feet higher than the road surface.
The style of the three arch structure, constructed from local fieldstone, predates the use of most covered bridges. Its seven and nine foot high arches were constructed using wooden frames, with seven visible metal tie rods (housed in metal shells) giving additional support. Once the arch keystones were placed, the wooden forms were removed. Two stone “icebreakers” jut from the area between the arches on each side.
Nine similar bridges were built in Adams County prior to 1825, but at the time of application, only two were surviving. The style is noted for its durability, but a newspaper article in 1972 noted consideration for replacing the structure with a modern structure. This was obviously not carried out, but major rehabilitation efforts in 2005-2006 were taken by Mechanicsburg’s Pennoni Associates, Inc., at a cost of $840,000.
From both a cost and historic perspective, rehabilitation was deemed preferable over replacement. The bridge’s location along a floodway provided challenges to the structure throughout its life, as well as to the rehabilitation process. Flooding probably led to much of the structural problems, and in particular, a weather event in January of 1996 led to a flooding and freezing cycle that led to numerous cracking issues. One of the primary improvements was the installation of precast concrete “backing blocks” that strengthened the arch structures and allowed the removal of a previous 15 ton weight limit on the bridge.
The project was deemed a success to the degree that the Association for Bridge Construction awarded it an Outstanding Rehabilitated Bridge designation. The National Cooperative Highway Research Program includes it as a case study in its guidelines for historic bridge work.
The bridge is noted in the NRHP nomination form for its representation of local stone architecture, as well as its part in a rural community centered around a mill and stream. It originally was located with twelve stone homes dating before 1850.
John’s Burnt Mill Bridge is one of 33 Adams County locations noted in the National Register of Historic Places, and one of five Adams County bridges on the list.
National Register of Historic Places Nomination Form - #74001731
U.S. Department of the Interior
National Park Service
Historic Bridge Foundation
Center for Environmental Excellence