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 -- SASIG Ed. ]

Scientist probe mystery mound at Mesa Verde
May 25, 1997

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.