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Hovenweep National Monument is located in the Four Corners region in a very remote series of canyons on Cajon Mesa. With sweeping horizons and open skies, the large concentrations of freestanding masonry towers are the only interruptions in the southwestern landscape. Holly Tower was constructed around 1200 AD atop a large detached sandstone ledgerock in the center of a deep canyon. It is often considered the most impressive of the Hovenweep structures and one of the best preserved. While the towers have been subjected to multiple stabilization campaigns since the creation of the National Monument in 1923, the condition of the Holly Tower support rock has been largely ignored in previous surveys. Today the support rock’s accelerated erosion threatens the foundation of the tower above, prompting an in-depth study of its decay and treatment.

  image of Square Tower
historical precedent NPS stabilization campaign, 1948. Hovenweep National Monument Museum Collection, Catalog number 18721, Collection 404, Series 001, File Unit 68.

Following the loss of a large slab of rock from the northwestern corner of the monolith, the National Park Service contacted the Architectural Conservation Laboratory to fully investigate, document, and develop treatment recommendations for the support rock in order to stabilize it and protect the foundation walls of Holly Tower. This project was modeled off of a similar problem that occurred at Square Tower in the 1990’s. Due to moisture-related issues in Little Ruin Canyon, the main group of ruins at Hovenweep National Monument, the sandstone support rock underneath Square Tower was experiencing large-scale surface erosion and this was mitigated through surface consolidation using an ethyl silicate product. This important precedent helped to develop a conservation plan for the support rock under Holly Tower, which experiences similar deterioration patterns.

  image of Square Tower
  NPS stabilization campaign, 1948. Hovenweep National Monument Museum Collection, Catalog number 18721, Collection 404, Series 001, File Unit 68.

 

 

 
Panorama view of the Holly Group site looking northwest. From left: Holly House, Holly Tower, Tilted Tower. ACL, 2012.