Canyon Sketches Vol 09 - March 2009
Archeologists excavate two sites along Colorado River
by Allyson Mathis
Grand Canyon National Park and Museum of Northern Arizona archeologists excavated two more archeological sites along the Colorado River as part of multi-year project.
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.
In September 2008, crews excavated an ancestral Puebloan site near Unkar Delta. Unkar Delta is the most extensive habitation site in the Colorado River corridor. In 1967 and 1968, the School of American Research, under the supervision of Douglas Schwarz, excavated 31 of the 52 identified sites at Unkar Delta. Unkar Delta was inhabited during the Formative time period mostly between 1050 and 1150 AD, which corresponds to the ancestral Puebloan, or Anasazi culture.
The site near Unkar Delta was first recorded in 1988 by archeologists. It is informally known as “Ivo’s site” as it was initially reported by now-retired US Geological Survey geologist Ivo Lucchitta. The site consists of several masonry walls, including a wood post that was eroding downslope, stone-lined storage cists and associated artifacts. Grand Canyon National Park’s Archeology River Monitoring Program has monitored the site annually since 1992 and has noted continued damage to the site primarily because of surface erosion and gullying.
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.
All features were filled with hillslope debris and very few artifacts were found. Lisa Leap, Grand Canyon National Park archeologist and excavation project co-director, explained, “The extent of the erosion at the site explains why we found relatively few artifacts. It appears that most of the midden, or refuse area, has eroded away. The site probably had a typical Puebloan layout with room blocks with a midden and activity area, but what we saw in our excavation consists of only what hadn’t been completely lost to erosion.”
During their work at the site, archeologists recorded nine additional features in the site, including a masonry room and several small slab-lined features. The largest room the crew excavated, Feature 8, was found in 2006 immediately adjacent to one of the known features when the project co-directors Lisa Leap and MNA archeologist Ted Neff evaluated the site for excavation. Feature 8 is a square room with a hearth and ventilator shaft that was probably used as an occupation room or as a kiva, which is a ceremonial room.
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.”
The crew built stabilization rock-work adjacent to prehistoric masonry for three of the structures they excavated prior to backfilling because it appears that arroyo-cutting will continue at the site. Leap explained, “We excavated this site because of the extent of erosion here. Data collection does allow us to learn about the people who lived here more than 800 year ago, yet we want to preserve as much of this site as we can, and hopefully the stabilization rock-work will help.
"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.
Leap said, “We excavated three units during our work in October, and identified and excavated 32 new features, mostly hearths.
"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.”
To date, crews have excavated six of the nine sites scheduled for excavation.
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.”
Leap continued, “We are really learning so much in this project. For example, based on the excavations at Unkar Delta and at Bright Angel Ruin near Phantom Ranch approximately 40 years ago, we thought that kivas were very rare in the river corridor. Yet we’ve found at least one and as many three kivas in the handful of sites we’ve excavated. Also, archeologists recovered only five stone pendants during the excavations at Unkar Delta. We found many stone pendants and evidence that people were manufacturing them in another site we’ve excavated.
"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.