Protecting the Canyon’s Ruins

One of the most interdisciplinary research ventures sponsored by gcmrc launched from Lees Ferry on May 4, 2003. The research group of geologists and archeologists—including representatives from the US Geological Survey, UC Santa Cruz, Grand Canyon National Park, the Hopi Tribe, the Hualapai Tribe, and Western Area Power Administration—set off to see the effect of Glen Canyon Dam on the sand that has been preserving Native American archeological sites. After examining the arroyos that are formed by water running down the canyon walls and seeing the archeological sites exposed in the arroyos, there are two questions on everyone’s minds. If Glen Canyon Dam didn’t exist or was operated to allow more sand to be retained in the system, would more sand be blown in from the bars along the river to fill in the arroyos? If there were more wind-blown sand, would it be slowing or preventing erosion of the ruins?
At the time the dam was built, environmental concerns focused on the area that was to be submerged beneath Lake Powell, upstream from the dam. Later, the Environmental Impact Statement (March 1995) for Glen Canyon Dam operations identified water, sediment, fish, vegetation, wildlife and habitat, endangered species, and cultural resources as some of the issues to be analyzed in detail, and studies have documented a number of impacts to the Colorado River downstream from the dam, below the high water line. There has been relatively little research on impacts above the old high-water zone. The archeologists and geologists on this trip are concerned that the dam may also effect that environment. The river corridor contains nearly 500 places of past human activity. The Grand Canyon Protection Act of 1992 mandates that Glen Canyon Dam be operated to protect downstream natural and cultural resources. If the dam operations have directly contributed to the erosion of cultural sites in the canyon, dam operations may need to change or other measures taken to ensure preservation of those resources.
Jan Balsom, National Park Service Cultural Resources manager, explains to the assembled group of scientists that 10,000 years of human history may be buried in the sands of the Grand Canyon. “With active arroyo cutting of archeological sites, many sites have recently been exposed, creating a huge problem for preservationists.” Can the creation of arroyos be slowed and the archeological sites preserved? What the Park Service wants, Balsom makes clear, is a “system-wide” strategy that will relieve her staff from trying to repair every exposed site individually. For the two-week trip, the archeologists pick more than 30 representative sites to visit, revealing a range of problems.
One stop is a site that National Park Service archaeologists have monitored over the past 20 years, and they have reported that each time they return, more artifacts are exposed. The archeologists have identified the site as being occupied approximately 900 years ago. It is impossible to walk without stepping on pottery. There are several identified ceramics, including Tsegi Orange Ware distinguished by its bright red color with black lines and flecks of white. There is a type of burned clay used in house construction known as daub. For a brief instant, the geologists forget about sedimentary structures, becoming amateur archaeologists, looking for artifacts and evidence of the past.
Each day, rising with the sun, the scientists trek across beaches, past blooming milkweed and blossoming cactus. They hike along sandy paths, walk over river terraces and onto rocky ledges overlooking the river. At one site, Balsom shows the top of an arroyo cutting into the posts and roof beams of a 1000-year-old structure. She explains that a structure even older is revealed below. At site after site, the scientists see fire-cracked rock, fire pits used to roast agave, ceramics, and carved and worked stone known as lithics. At one site where there is no visitor traffic, whole terraces are filled with archeological sites, and potsherds are scattered across the landscape. At other sites the archeologists show off check dams built by the Zuni Conservation Program. Some look like random scatterings of driftwood, others look like piles of rocks, all are placed to stop erosion, trap wind-blown sand, and prevent exposure of nearby artifacts and structures.

David Rubin, a u.s.g.s. sedimentologist, directs the geologic research. The question for the geologists is whether the sand up on the plateaus, at the edges of the beaches, and atop the sand dunes is fluvial or eolian (whether the sand was deposited by water or wind). With shovels, trowels, Brunton compasses, and a Chinese calligraphy brush, the geologists march up and down the beaches, looking at the sedimentary structures in the cutbanks. At one site not far from the water’s edge, Rubin sees ripples migrating right to left and upward, and identifies them as fluvial climbing ripples. At another site, the geologists agree that the sand is probably fluvial, either from a 300,000 cfs flood of the Colorado River, or from flooding of a nearby side creek. At the next site, closer to the river, and lower on the plateau, all agree that the 10 foot wall of mud, pebbles, and rocks is from the side creek.
But many sites show evidence of eolian sand deposition. Wind-blown sand is found on the beach near the water’s edge, and up in canyons, far from the river. At one newly exposed site, Rubin considers that “if the sand bars were bigger, less vegetated, and less frequently submerged, more sand would blow up the canyon and up to the area of this site.” The geologists look at another site and consider the incredible amount of sand and wind it would take to provide protection to the area, noting that the sand would need to travel quite a distance from the river, blowing over boulders, reaching well above water level. But Balsom recalls seeing sand dunes form up on the ledges of the Redwall Limestone, well above river level. Other researchers recall times in the canyon when the wind is blowing so hard the sky is sand-colored, when the wind blew sand into their eyes while they rafted down the middle of the river. The geologists note that the cactus and bushes in the area all appear on mounds that are being undercut, a sign that there used to be a lot more sand in the area. Their examination completed, they agree that with the 40-50 mile wind gusts common in the spring, and with more sand in the system, it might be possible for eolian sand to reach up to the sites that are now being exposed.
Another site has extensive pottery scatter and is believed to have been occupied during much of the time from 900-1640 ad. Seven cultural features had been identified at the site. Four have already disappeared, victims of erosion. The scientists all agree that the site is a good place for an excavation to integrate the sciences of archaeology and geomorphology.
The preliminary investigation completed, several of the geologists think that reduced wind-blown sediment might be a significant factor causing erosion of the archeological sites. To determine whether the dam is, in fact, depleting the sand source, the geologists outline the investigation. Geologic maps and air photos will be used to determine a site’s position in the larger landscape. Anemometers will be placed to record winds and sand traps will be set to measure transport of wind-blown sand. Historical photos and statistics from completed surveys will be used to compare bar size and vegetation over time. Amy Draut will conduct this research for her post-doctoral fellowship funded by gcmrc.
The investigation is wide-ranging. On a small beach, the grasses have grown into a 10-foot-tall, nearly impenetrable barrier, covering all but a narrow15 foot strip of sand at the water’s edge. The role that these new plants play in the preservation or erosion of archeological sites is unknown. If the vegetation were removed (or at least reduced) and the sand bar made bigger, would more sand be blown up to the archeological sites above the high water line of the river? Or would the beaches and arroyo banks erode further without the vegetative protection, further reducing the sand available to protect the archeological sites? Until now, the geologists have considered the role of the vegetation only when lamenting the loss of good camping beaches and when cataloging the changes that have occurred since erection of the dam. The analysis changes if the vegetation is either protecting or harming the archeological sites.
On the river, the water is incredibly clear. In the shallow places, individual rocks on the bottom of the Colorado are visible. The sparkling water confirms that the canyon is depleted in sand and mud. A little later, the water clouds slightly, confirming that sand is being taken off the already depleted beaches. Does this sand get washed completely out of the canyon, or does it end up on downstream beaches, where it might blow onto archeological sites?
With so many archeological sites at stake, the study’s conclusion is being excitedly anticipated.

Michelle Rubin