The National Park Service has come up with a plan to save Spruce Tree House/Rebecca Latson file

Rock bolts and reinforced concrete supports are among the tools the National Park Service wants to employ to stabilize the alcove in which Spruce Tree House stands in Mesa Verde National Park in Colorado. The plan, developed over the past year as the agency debated how to keep the sandstone arch from further collapse, could be implemented in September and continue through next winter.

The popular attraction, which houses the third-largest cliff dwelling in the park, with 130 rooms and eight kivas, has been closed to the public since October 2015 because of concerns that layers of sandstone could peel away from the arch at any time and fall on bystanders below. Spruce Tree House may be seen, however, from an overlook near the Chapin Mesa Museum. 

Back in 2016, the Park Service pointed out that "[E]arly stabilization work was performed (on the arch) in the 1940s, with additional stabilization work completed in the 1960s. Natural erosion processes, including the settling of the arch, have been affected by the early stabilization work, so that modern engineering techniques may be necessary to ensure continued stability of the arch."

Under the preferred proposal contained in an environmental assessment now open for public comment, up to 75 20-foot-long tensioned rockbolts would be installed in a net-like pattern to stabilize the overall alcove arch. This approach creates a three-dimensional network of steel reinforcement that stitches and ties together individual preexisting rock blocks within the stabilized overall rock mass, thus forming a unified “rock block," the EA notes.

Additionally, the project would involve:

• Installation of 120 passive 6- to 8-foot rockbolts to stabilize smaller local rock features.
• Encapsulation of every completed rockbolt with custom-colored mortar that would match the color and texture of the adjacent surrounding sandstone and provide corrosion protection.
• Treatment of shrinkage cracks in the existing concrete plug (installed in 1963) between the sandstone at the back of the alcove arch and the outer face of the alcove roof.
• Removal of loose surface rocks, detached rock slabs, and vegetation (minor scaling) using hand and power tools.
• Installation of several relatively small, rectangular-shaped corbels6 (constructed of reinforced concrete and color matched to the local sandstone) that would be tucked up and under several hanging rock blocks that form part of the alcove’s outer surface. Their position would minimize exposure and visibility.
• Installation of geotechnical instrumentation with remote data logging and transmitting capabilities (located in the park’s headquarters) to constantly monitor the alcove arch’s stability.

Public comment is being taken through April 10. You can find the EA and a page to comment at this site.

Under the preferred alternative, the cliff dwelling would reopen to the public after the work is completed. The EA also contains a "no action" alternative, which would keep the dwelling closed and allow natural processes to contine to eat away at the alcove, and an option to prevent continued deterioration but not reopen the dwelling to the public.