Message #213: From: AzTeC SW Archaeology SIG To: "'Matthias Giessler'" Subject: Mesa Verde Mound Is A Reservoir Date: Wed, 04 Jun 1997 21:43:45 -0700 [ See the Colorado 1997 Archaeology and Historic Preservation Week poster at http://www.durangoherald.com/news628.htm -- SASIG Ed. ] http://www.durangoherald.com/news706.htm Scientist probe mystery mound at Mesa Verde May 25, 1997 SPECIAL TO THE HERALD/SCOTT WARREN PROJECT LEADER Kenneth R. Wright, the 68-year-old president of Wright Water Engineering Inc., vowed to solve the riddle of the Mesa Verdeās 200-foot-diameter mystery mound that had divided scientists for decades. His company and a state grant paid for last weekās dig, which involved this 140-foot-long and 15-foot-deep trench through the mound. By Electa Draper Herald Regional Editor It was a centuries-old puzzle in dirt that scientists believe they finally solved. From a ridge overlooking Morefield Canyon, one can view almost the whole of the mysterious earthen mound, 200 feet wide, that rises 15 feet above a grassy floor now filled with the white blossoms of mountain mahogany. Locked away from the hordes that drive and traipse through Mesa Verde National Parkās developed areas, the rounded formation was a sage-covered enigma that archaeologists and other scientists had argued about for decades. Some said the mound was a ceremonial platform of the ancestral Puebloans (formerly called by the Navajo word "Anasazi"). Some said the mound was an eroded remnant of a geological formation. Others judged it was exactly what the convex shape didnāt resemble ö an ancient reservoir raised above an arid canyon floor that is host to a stream that rarely flows. It turns out the improbable-looking solution fit the clues unearthed last week by a multidisciplinary team led by Kenneth R. Wright, the 68-year-old president of Wright Water Engineers Inc. Wright believes the mound is a reservoir of the Pueblo II period, A.D. 900-1100. Everyone at the site was personally convinced of it, he says, after four days of excavation, May 16. It was a massive public works project for that era, Wright says. The reservoir was off-channel, built to the side of the canyonās ephemeral stream. It was fed by what ultimately became a 1,400-foot-long canal that intersected the stream higher in the canyon. Wright, known for his work on ancient waterworks in the Incan city of Machu Picchu in the Peruvian Andes, admits he is surprised these vanished Southwest Colorado natives could have constructed a project of this scale. "Something this big doesnāt come easy," he says. The massive canal also was built up to 15 feet above the valley floor and stream bed, its steep sides shored with beautifully aligned large stones of a sort a team geologist says are not found in this canyon. John Rold, a 69-year-old former Colorado state geologist, hazards a guess the canal might have been 4 to 8 feet wide and perhaps was only 1 to 2 feet deep. The canal has a 1 percent gradient ö like modern irrigation works, it falls 1 foot in elevation for every 100 feet it traverses. Even though it is only mid-May and Morefield Canyon is at its greenest, the stream bed is dry. The ancient inhabitants planned and built, Wright believes, to capture the rare big rains that would roar through the canyon every couple of years. But why would a reservoir resemble a giant dirt pie? Team member Eric Bikis calls it the inverted frying pan because the canal resembles a long handle. Wright and the 20 or so experts and other volunteers on the project think the flash floods transported a lot of sediment that quickly filled the reservoirās depression. The canyon inhabitants attempted, with crude tools, to push out the sediment filling the basin, the scientists speculate. Wrightās group found evidence of small berms that would be formed by dirt scooped out of the reservoir and left along its shore. In this way the inhabitants built up the level of the reservoir, Wright says, and they kept reworking the canal so it would intersect the stream farther and farther up the canyon and so still feed their elevated impoundment. Wearing a blue hard-hat with four stars (presented by a crew well aware of his skills as field marshal), Wright cautions that more analysis of data is needed for definitive results. Proof is far different, he says, than the educated guesses flying around the dig last week. The dig had been preceded by roughly two years of reconnaissance surveys and studies on the mound. Wright, whose Denver-based company and a Colorado Historical Society grant paid the projectās $35,000 in expenses, decided it was finally time May 13 to slice open the mound and get to the bottom of it. Wright harnessed his resources ö people, like Rold, who donate their expertise and time for the pleasure of solving an earthen riddle. Many of the team members work for Wright Engineering. "It sharpens our skills in everyday work," Wright says. "It helps teach our people discipline and focus." Bikis, a 42-year-old hydrogeologist who works for Wright out of Durango, says the common bond is curiosity. "No one is here because they feel obliged," Bikis says. The mound had been just one of hundreds of ancestral Pueblo sites found in the park for which there has been neither time nor money to fully investigate. But Wright believes the mound is unique, and thatās why he vowed to solve the puzzle. Nothing like it, raised above the floor the way it is, has been found elsewhere in the park, he says. Thirty years ago, the mound had captured the attention of a University of Colorado professor,Jack Smith, who later served 15 years as the parkās chief archaeologist. Smith was thwarted in his 1967 attempt to reveal the secret of the mound, and he returned to tackle it again this May as part of Wrightās team. On May 17, Smith, now 67, looks happily into the depths of a trench arcing gracefully for 140 feet, populated by archeologists, soil experts, sedimentologists, hydrologists and geologists laying down a grid, flagging points, collecting soil samples and potsherds. The trench, with its stepped sides, is about 16 feet wide at the top but very narrow at the bottom and, at times, a little crowded. Smith recalls his earlier attempt at the mound. His team tried to cut a trench through it, he says, but instead of having a large backhoe that could bite hard and move dirt out of the way, the project then had only a front-end loader. The operator started trenching on two sides of the mound, hoping the gashes begun opposite each other would meet in the middle. But they werenāt aligned, Smith says, and the equipment just couldnāt make it across the expanse. Smith had run out of resources and time in the field. But he saw enough to suspect, he says, against his earlier intuition, that the site had been a reservoir. However, his findings in ā67 were inconclusive. He never thought heād get a second crack at it, he says. One of the parkās conditions on Wrightās project permit was that the new trench had to follow as closely as possible the scar of the old trench, which threw the modern investigators a curve. A straight cut is much preferable because scientists want to make a near-perfect grid, record precise origins of samples and correlate findings on opposite walls of the trench. It is all harder to do in an arc, but they do it. "Weāre going to try to answer questions from three or four different angles," says 42-year-old soil expert Doug Ramsey, who works for the U.S. Natural Resources Conservation Service in Cortez. Ramsey says the team can show the mound is not a remnant of a naturally formed terrace as some supposed. That formation would be 10,000 years old, and the team found pottery shards, only several centuries old, 12 feet deep in the mound. Ramsey holds up a clod of dark earth mottled by a rust-colored stain. "This iron staining happens under saturated conditions ö standing water," he says. Down the wall of the trench, layers of rough clay alternate with ribbons of smoother sand. The silty layers, some very thick, were deposited by flood events in a short time, perhaps a couple of days, Smith says. "You can get a good gully-washer through here every couple of years," he adds. The clay layers were deposited in between and may have taken many years to accumulate. Only water could have laid down these sediments, Bikis says. The impermeable clay lining of the reservoir likely protected it from losses through seeps. On May 18, Ramsey probes about 5 feet lower than the trench floor to finally reach the siteās native soils. This tells him the mound started out as a more normally configured reservoir, dug 5 feet below the canyon floor. Then, a short ditch to the stream likely sufficed as the water source. Smith estimates ö he calls it a guess based on the number of ruins scattered throughout the canyon ö that perhaps 500 people once lived here. "Weāre not sure why they selected this site in the canyon," Bikis says, "but we know they were very observant, very water-wise." Just down the valley from the reservoir site is a great kiva, 50 feet in diameter, that is the largest known kiva in the park, he says. It was excavated and refilled because there were no resources to restore it. By May 19, the excavation of the mound was over ö the trench filled, probably never to be reopened, and the known history of the ancestral Puebloans grew richer.