Hoosac Tunnel Ruins Mapping Project
Alignment Tower Site Ruins Above the East Portal
Above the East Portal of the Hoosac Tunnel, surface evidence of the alignment system used during excavation remains fixed in place along the projected line of the bore. What survives is not a single structure, but fragments of a larger measuring network once stretched across the mountain.
On Spruce Hill, the remaining material consists of the lowest course of a stone alignment tower. The masonry rises only slightly above grade and is partially embedded in soil, leaf litter, and seasonal debris. No superstructure survives. The stones mark the base of a tower erected to hold optical instruments used to maintain a straight line of excavation over the mountain. Later disturbance to the area, including power line installation associated with the Central Shaft vent building, likely accounts for the removal of the upper portion.
On Rowe’s Neck, just east of the East Portal, the alignment point takes a different form. Four heavy iron spikes remain driven directly into exposed bedrock, defining the footprint of a survey platform at that location. No masonry is present. The absence of stone debris suggests a structure built primarily of timber, mechanically anchored rather than constructed as a permanent stone tower. Only the iron elements remain, preserved by material rather than intention.
From this position, the alignment extends across the Deerfield River valley toward the East Portal and bridge. Dense vegetation now interrupts direct sightlines, but the spatial relationship between sites becomes readable during reduced foliage. Looking upslope from the portal area, a faint linear scar on the mountainside traces the former Western Union pole line that once carried communications and power supporting tunnel construction.
These features document how alignment was maintained over many years of excavation. Fixed reference points were established on the surface, repeatedly measured, and used to transfer a straight line underground through bedrock. Once their role was complete, the towers were dismantled or allowed to decay, leaving only stone bases, iron anchors, and scars in the landscape.
In total, six alignment towers were constructed across Hoosac Mountain to accomplish this task. Working together, they formed a continuous surface geometry that allowed crews digging from the east portal, west portal, and central shaft to meet with extraordinary accuracy for the mid-nineteenth century.
This documentation forms part of the ongoing Hoosac Tunnel Ruins Mapping Project, focused on identifying and recording the surface infrastructure that made underground excavation possible. You can find all my content on the Bloody Pit, including long-form features and podcasts, on
Restoration Obscura.
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