Total collapse
Mesa Verde faces big task to save prized cliff dwelling

Total collapse

Mesa Verde National Park will attempt to stabilize the overhanging rock arch above the popular Spruce Tree House cliff dwelling to remove the risk of it collapsing and damaging the ruins below./ Courtesy of National Park Service

Jonathan Romeo - 12/23/2021

It’s not going to be easy: Mesa Verde National Park is about to try and stop a massive slab of sandstone from collapsing and destroying one of the most prized cliff dwellings in the park, Spruce Tree House.

In October 2015, park officials were forced to close Spruce Tree House to visitors after a series of rock falls made it too dangerous for people to enter the iconic alcove. Mesa Verde is home to some of the most notable and best-preserved cliff dwellings in the world, but Spruce Tree House, the third-largest cliff dwelling in the park, is by far the most visited because of its easy access.

The ancestral Puebloan people built these massive and thriving communities between the years 900-1250 in protected alcoves – large, arched recesses in the cliff wall. But, over the years, park officials have been concerned the rock structures above and around the alcoves are increasingly at risk of erosion and other geological forces.

For the past six years, Mesa Verde has undertaken an exhaustive effort to figure out how best to stabilize the failing sandstone above Spruce Tree House – not just to make it safe for the public, but also to save the cliff dwelling underneath. Those plans are coming together, said project manager Allan Loy, but there’s still a ways to go.

Preserving the past

Most national parks receive such a designation because of natural beauty and sweeping landscapes. Mesa Verde, on the other hand, was the first national park established specifically for the preservation of the “works of man” – i.e. the ancestral Puebloan’s civilization.

For more than 700 years, the region around Mesa Verde was a robust and thriving community, with hundreds of villages and more than 22,000 people (almost the same population as today). Around 1250, however, the region was mostly abandoned, likely due to climate issues and/or social disruptions.

In the 1870s, the first white settlers discovered and started to understand the complexity of the vast network of ruins throughout the deep canyons and mesas of the high desert. (Of course, the Ute people were actively living in the region at the time, but did not inhabit the ruins, believing them sacred).

Subsequent research expeditions revealed more amazing truths about Mesa Verde, but also brought on a disturbing amount of looting and destruction of sites. By the end of the 19th century, it was apparent the region needed federal protections. The park was established in June 1906, protecting more than 4,300 cultural sites, including 600 cliff dwellings, within the 52,000-acre national park.

Crumbling curio

From the beginning, archaeologists were alarmed about the imminent risk of rock fall to Spruce Tree House, with the first concerns documented as early as 1908.

Spruce Tree House is home to 130 rooms and eight kivas, and lies within a natural sandstone alcove that’s 216 feet long and 89 feet deep. The issue at hand is water draining between the arch of sandstone overhanging the alcove, which causes erosion and poses the risk of the arch breaking off and collapsing right on the ruins. Early archeologists tried fixing this by blasting a trench in the sandstone to direct water to the sides of the structure, to no avail.

Attempts in the 1960s did accomplish temporary relief after the southern half of the arch was stabilized by rock bolts, anchoring the arch to the alcove. The crack was then cleaned and plugged with burlap and concrete. This was effective, for a time, until natural elements once again started eating away at the rock structure, resulting in the rock falls in 2015.

Park officials originally thought it would take two years to come up with a fix. But the complexity of the problem, as well as continued rock fall, has required more time for study. Mesa Verde hired one of the best geo-tech engineering firms in the world, Loy said, which has generated an incredible amount of research and study.  

Three-dimensional modeling, high-resolution Lidar, photogrammetry, on-site inspections, material testing – you name it, the park has done it, Loy said. The most vexing problem, according to studies, is how to fill the significant gap between the alcove face and the arch to prevent water from entering Spruce Tree House. 

It appears the fix is going to be multi-pronged. The park will likely use rock bolts again, but this time, installed at offset angles, which would increase strength (think of the root structure of a tree). And, new material, likely a type of metal, will be used to fill the crack to stop water from entering.

“And we’ve been using a number of models to see where failures could happen in our designs,” Loy said. “And then we ensure our design compensates for it.”

The crown jewel

Spruce Tree House has always been the centerpiece of Mesa Verde, said Fort Lewis College professor and historian Andrew Gulliford. Centrally located in the park, and surrounded by facilities like a museum and the superintendent’s house, the cliff dwellings are also relatively easy to get to compared to other sites. As a result, the ruins are one of the most important educational pieces in the park, with most people who enter Mesa Verde visiting Spruce Tree House.

“Not only are there centuries of human habitation by the ancestral Puebloans, but now there’s 100-plus years of visitation,” Gulliford said. “That part of Mesa Verde is so important for so many reasons.”

But as time wears on, it is just an evident reality the elements will claim relics of the past. Increasingly, descendants of the ancestral Puebloan people have voiced a desire to not interfere with this natural process. At Mesa Verde, the park is required to consult 26 different tribes. Loy said it’s about a 55-45 split on tribes in favor of preservation efforts vs. letting nature takes its course.

Calls to the Acoma, Ute Mountain Ute and Zuni tribes were not returned for this story. 

Paul Reed, a preservation archeologist with Archaeology Southwest, said the debate to let ruins go through the natural cycles of decay and erosion has come to the forefront as tribes have been given more of a voice in recent years. “Which is way overdue,” he said. “That process alone is a vast improvement on more than a century of not consulting tribes.”

Spruce Tree House, however, presents its own nuances and case for preservation efforts, just because of the long history of accessibility to the site, and how important it is for the public to learn about the people of the past. It should be noted, the National Park Service (which just named its first Indigenous director, Chuck Sams) has a mandate to protect cultural sites.

100-year solution

The American Southwest can be a harsh landscape. Even the Native people at Chaco Canyon built safety structures around Pueblo Bonita to protect the village from a 30,000-ton block of sandstone that was at risk of toppling over. That rock, fittingly called Threatening Rock, came down in the 1940s and took out a considerable portion of the ruins. And even now, there’s an ongoing attempt to save Pompeys Pillar, a rock in Montana with inscriptions from the Lewis and Clark expedition, which faces erosion issues.

“People have been trying to fight nature for a long time, especially when it comes to ancestral Puebloan sites,” Shanna Diederichs, architectural conservator at Woods Canyon Archaeological Consultants, based in Cortez, said. “Today, we’re fighting the same problem, and what you’re seeing is a desperate play to save these sites.”

What the Park Service is attempting is not unheard of, but because the geology of Mesa Verde is specifically unique to the region, there are really no other examples to draw from. In fact, only a few people are even qualified to attempt it, Diederichs said (she is not involved in the project but has worked at Mesa Verde). “It’s been six years since Spruce Tree House was closed, but it’s been under discussion for almost 100 years. It’s irreplaceable and worth saving. That’s why such a crazy effort is going into it.”

If all goes according to plan, Mesa Verde hopes to start construction on Spruce Tree House in October 2022, and hopefully, reopen the site to the public in summer 2023, Loy said. But it’s going to be a long road to get there, with a National Environmental Policy Act process required. Loy said he was unable to provide an estimate of how much the project is expected to cost.

Mesa Verde was on track for high visitation during the last fiscal year, cresting over 610,000 people. But the park believes visitation will suffer if Spruce Tree House doesn’t reopen. So, Loy said, part of the plan is to have active monitoring equipment installed, so when visitors are allowed back in, the park can see real-time data for any risks of rock failure.

“I know people are definitely interested in Spruce Tree House reopening,” Loy said. “And when all is done, we’re looking at a 100-year solution.