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Canyon Sketches Vol 09 - March 2009
Archeologists excavate two sites along Colorado River
by Allyson Mathis
A total of nine severely eroded sites will be excavated along the Colorado River corridor. The sites are being excavated because they are too extensively eroded to be preserved in place, making the data recovery efforts the only viable option for park managers.
A slab-lined cist was destroyed by erosion in 1995. In 2002, part of a masonry wall associated with charcoal and burned beams was exposed by erosion in a side canyon.
During their 10-day field session in September 2008, archeologists excavated the six known features at the site, and documented additional features there.
Crews also excavated a kiva in 2008 at a site a few miles upstream of Ivo’s site.
Leap said, “While we found few artifacts in Feature 8, there were well-preserved wood beams and posts that we sampled for dendrochronology, or tree-ring dating. Dendrochronology is useful in archeology because it tells us when the tree died, which in many cases we assume to be the time when a tree was cut down and used in construction.
"However, given that large trees are rare in the inner canyon, and the fact that this site is directly adjacent to the Colorado River, it is likely that the people utilized drift wood for posts and beams. Therefore, we are using as many techniques as possible to date the sites we are excavating in the river corridor, including dendrochronology, carbon-14 dating, and optically stimulating luminescence or OSL dating which tells us when the sites were buried by sediment.”
"We carefully documented the stabilization rock-work with photographs, maps and surveying equipment to record what we did and to allow archeologists who will continue to monitor the site to differentiate our work from the original masonry,” said Leap.
Axehandle Alcove Site
In October 2008, archeological crews excavated the Axehandle Alcove site which is one of the few deposits remaining in Grand Canyon that preserve a long record of Colorado River floods.
The site is located to the inside of a large recirculation eddy and is protected by a large cliff overhang. The sediment at the site records at least 25 different Colorado River floods that occurred during the last 5,000 years. The fine flood-deposited silts are interlayered with coarser debris eroded from the surrounding cliffs. A deep arroyo has cut through this unique deposit eroding cultural material such as charcoal lenses and hearths present in the sediment.
This site is the oldest of the nine sites being excavated in the current project. There are no structures present within the site, and the only ceramic artifacts found were on or near the surface.
Archeologists also recovered some stone flakes that had been utilized as tools, a stone drill, a bone awl, and ground stone that may have been used to process food.
Archeologists have provisionally identified six periods of human occupation at the site, ranging from Late Archaic, at about 4,500 years before present, to the Formative period, approximately 900 years ago.
"Because this site lacks structures, it may seem unremarkable to the untrained eye. But the site is very important archeologically because it spans a time period where there are relatively few archeological sites in Grand Canyon and spans the transition from foraging to sedentary life-styles which are dependant on agriculture.
"Additionally, the stratigraphy at the site will allow us to reconstruct the paleoflood history as it relates to human use of the area. Charcoal that we and previous researchers have recovered from the hearths allows us to date the floods and the periods of human use of this site very well.”
While the artifacts recovered during the excavations are still being analyzed in the laboratory, archeologists have arrived at some preliminary conclusion.
Leap said, “One of the things we’ve learned so far is that prehistoric people lived on the same general landscape that we see today along the Colorado River corridor in Grand Canyon.
"We’ve also learned that each site that we’ve excavated to date is unique, each having its own history of erosional and depositional processes that have impacted it through time.
"For example, the structures at Ivo’s site were buried by debris washed down the hillslopes, whereas other sites were buried by aeolian, or wind-blown, sand. At the Axehandle Alcove site, river flood deposits have preserved cultural material that otherwise would have eroded away.”
"Another site yielded the earliest and most definitive evidence for the cultivation of cotton at Grand Canyon.”
Archeologists will excavate three additional sites in April and May 2009 and will continue to learn more about the peoples who called Grand Canyon home in the past.
Grand Canyon National Park Archeological Resources
The River Monitoring Program
generates data regarding the effects of Dam operations on historic properties, identifies ongoing impacts to historic properties within the APE [Area of Potential Effect], and develops and implements remedial measures for treating historic properties subject to damage.
Did You Know?
Yavapai Geology Museum, features geology exhibits that allow you to see and understand the complicated geologic story that is Grand Canyon. More...