Due to the possibility of rock fall, Spruce Tree House is closed.
Spruce Tree House, the best preserved cliff dwelling in Mesa Verde National Park,
is the third largest site in the park with a total of 120 rooms, two towers and 8 kivas.
Spruce Tree House was primarily occupied from A. D. 1206-1280,
part of an extended community which included other cliff dwellings and mesa top villages.
Early explorers named it for the trees found in the canyon bottom below the alcove,
Douglas-fir, also known as Douglas-spruce.
Two years after the park’s establishment, in 1908,
the site was excavated and stabilized by Jesse Walter Fewkes of the Smithsonian Institution.
The stabilization efforts by Fewkes included blasting a trench in the rock above the dwelling
in order to reroute the flow of ground surface water, which keeps it from
cascading over the rim onto the dwelling below.
This blasting, however, may have disrupted a naturally-occurring arch in the cliff-face,
causing it to settle an additional few inches.
The arch is part of a 270-foot long crack that parallels the rim above the site.
The crack measures a mere few inches to 5 feet at its widest.
The arch section is visible from both the canyon rim as well as from within the site itself.
The crack was originally stabilized by Al Lancaster in the 1940s.
His team cleaned, covered, and waterproofed the crack,
although it appears that these waterproofing methods were ineffective.
In the early 1960s, the possibility of the arch breaking free
prompted additional work to be done.
In order to prevent severe damage to the dwelling,
as well as to prevent harm to visitors on the trail below, the 1940 cover was removed
and forty-six rock bolts were installed to anchor the arch to the cliff behind it.
The crack was then filled with aggregate concrete and grouted.
Rock falls are not a new phenomenon for Spruce Tree House.
Archived reports show that this alcove is one of the most active of those open to public use in Mesa Verde.
Sandstone of varying degrees of hardness, alternating with layers of coal and shale,
form the canyons and alcoves.
Natural forces such as rain, snow, ice, and the growth of trees and shrubs
also contribute to alcove formation, and exert pressure on the arch.
As these forces work, they gradually erode and undermine the harder layers of sandstone,
which can fall in pieces weighing from a few pounds to several tons.
In 2015, a rock fall prompted a geotechnical engineering assessment of the alcove.
Preliminary results revealed the risk of continued rock falls,
especially along pathways into and within the site.
Until a full geotechnical assessment is conducted
and work is done to reduce this threat,
Spruce Tree House will remain closed.