Every year, millions of tourists visit the Grand Canyon of the Colorado River in northern Arizona and marvel at its mysterious beauty.
In June, a small group of earth scientists gathered at the Canyon to ponder its beautiful mystery.
Their discussions highlighted a remarkable irony: Although the Grand Canyon is the United States' most famous geological feature, geologists do not know for certain how it was formed.
And instead of providing an answer, the June symposium actually may have expanded the controversy over the Canyon's origins, according to Peter Huntoon, a groundwater geologist and retired professor of geology at the University of Wyoming.
"I was excited about this meeting," he said. "The new ideas presented there really hit the floor and were vociferously opposed by the old school."
In fact, several old schools of thought exist -- expressing a variety of viewpoints and geological theories -- along with a multitude of new ideas about the history of the Colorado River and the Canyon's formation.
Jill Savage, now working on her master's degree project at the Colorado School of Mines, also attended the meeting. She came away impressed by the quality of the geology presented and of the geologists present.
"It was interesting to a new, fledgling scientist to step into an atmosphere where people tried as much as possible to leave their egos behind," she said.
"It gave me an appreciation of the great geology being done in the Canyon and the importance of the problem they were trying to address."
Richard Young served as organizer and coordinator for the meeting, the Grand Canyon-Colorado Plateau Symposium, held June 7-9 at Grand Canyon National Park. Young is professor of geology at the State University of New York at Geneseo, N.Y., and has studied the Canyon area since 1962.
Tracing the development of the Grand Canyon presents a puzzle for geologists, Young explained.
A major quandary involves the course of the Colorado River. See figure 1.
Today, the river begins just west of the Continental Divide in north-central Colorado. It flows across the southeast corner of Utah, drops south into Arizona and passes through the Grand Canyon, then leaves the Colorado Plateau and extends west to Lake Mead and Nevada.
At that point, the Colorado runs directly south, forming the California-Arizona border and emptying into the Gulf of California less than 75 miles south of Baja California's northern edge. If the Colorado had followed that course from its beginning, it would have flowed up and across the Kaibab Uplift and other elevated topography -- in defiance of logic, as well as gravity.
Because of that problem, some geologists propose a precursor to the Colorado with a much different course. This earlier river would have encountered the Laramide uplifting and then turned to flow southeast or southwest, or even to the north.
"At the conference we just finished, one of the things we talked about was whether or not there was really enough evidence for an old Colorado River in the upper reaches," Young said.
In general, geologists acknowledge that the eastern Colorado River expanse appears much older than the Colorado flowing west from the Grand Canyon, a watercourse likely less than five million years old.
One widely held theory proposes an early Colorado that turned south short of the uplift and followed the path of the present-day Little Colorado River, but flowing in a reverse direction, to the southeast.
That river would have emptied into Lake Bidahochi, also called Hopi Lake -- at the time a significant body of water.
Hello Hopi Lake?
In this theory, another drainage system west of the uplift carried water across the Basin and Range. Over time, its headwaters cut a path through the uplift and eventually met and captured the ancestral Colorado.
But Young said subsequent research seems to contradict this explanation.
"Back-of-the-envelope calculations show it would take less than 100,000 years to fill (Lake Bidahochi) up with sediment," he noted. "Based on that, it's hard to see how you could run a river in there for a million years."
That doesn't convince Bob Scarborough, staff geologist at the Arizona Sonora Desert Museum in Tucson, Ariz. He has a different theory about the lake: Would it necessarily clog with sediment?
"If the old Colorado had the flow that it has today, that might be true," he said. "But what if we had a much smaller, proto-Colorado River delivering only a fraction of the force that the river delivers today?"
Scarborough envisions a different kind of Hopi Lake, one fed by the Little Colorado drainage system and perhaps even the Puerco River, bringing water down a "paleo-drainway" from the mountains of southwest Colorado.
"There is evidence throughout the eastern part of the Little Colorado valley that there was a lake there," he said.
This lake was about 6,000 feet high, Scarborough theorizes, and he has contoured the lake's northern reaches.
"That contour line tracks right to the top of the Kaibab sandstone, and that is the lip of an old dam," he said. "I'm working on the hypothesis that this lake built up and built up and overtopped the lip of this dam into the Grand Canyon."
In part, Scarborough bases this theory on study of the Little Colorado River Gorge near the Grand Canyon. As the lake drained five million years ago, he believes, the torrent of water carved out the gorge as it fell to the Canyon's level.
It also may have scoured out the Grand Canyon as it passed through. Scarborough said he "leans toward" the idea that the Canyon of that period was filled with gravel from erosion of earlier mountains.
A Couple of Camps
That assumes the prior existence of the Grand Canyon or at least a forerunner canyon, of course. Scarborough sees two camps of scholars with opposite views about the origins of the Canyon.
The first camp accepts the existence of a "proto-Grand Canyon," probably dating to the period of Laramide uplifting, according to Scarborough.
"The real advantage of that camp is having a way to get the Canyon cutting through the Kaibab Uplift," he said. "If you look at the structural relief on the Kaibab, it's incredible."
A second camp claims the entire Canyon was carved out in a very short time -- and Scarborough doubts that possibility.
"If you don't do it the way I'm looking at, if you don't have a pre-existing eastern Canyon, you have to start the Colorado River way up in the sky," he said.
To bolster his theories, Scarborough is looking for evidence of a Laramide meander belt, an ancient waterway that might have set the path for the Colorado River and helped establish the Grand Canyon.
"The Grand Canyon is really a two-part canyon -- a broad, flat-bottomed outside canyon incised by a steep-walled inner canyon," he said. "I'm guessing that inner canyon is youthful."
Vital clues may be washed away, displaced or missing, however. Scarborough sees some evidence for older flow, but added, "it's a moot point. The only evidence out in the western Grand Canyon is for young flow."
After studying the Canyon for decades, Huntoon tends to dismiss elaborate theories of development as "convenience models," including the headwater-erosion hypothesis.
"There's a very entrenched dogma that's gotten into the science. That's the precocious gully theory," he said. "All the arm-waving you can do can't produce one shred of evidence that thing was there. And the mechanics of headwater erosion and stream capture don't work."
Huntoon said he participated in a field trip to the Bidahochi area that found not lacustrine deposits but fluvial, fine-grained clastics integrated with ash beds.
"This tells us that the Miocene was very dry on the Colorado Plateau," he said. "Consequently, there wasn't flowing water on the plateau. It looked more like the Mojave of today, with basins collecting sediments, and streams flowing in but not out."
But even Huntoon needs some kind of pre-existing canyon to get the Colorado across the Kaibab, as well as the Uinkaret and Shivwits plateaus.
"About half the existing depth of the Grand Canyon existed before the Colorado existed," he said. "Evidence implies there had to be something there."
Geologists who believe in a young Grand Canyon have a small window of time for cutting as much as 6,000 feet of rock from the Canyon's rim to its floor. At maximum stratigraphic depth, the Colorado cuts almost 1,800 feet into Proterozoic basement.
Fast Cut to the Finish
Studies presented at the symposium indicated such quick carving could be possible, according to Young.
"Coming away from the meeting, most people were impressed that you can do a lot of downcutting very quickly if you have to," he said.
Huntoon said the findings showed flows that "cut through volcanic bedrock like butter," and added, "I've been skeptical about it, but the dates keep proving me wrong. I'm having to rethink this whole thing."
To help solve the Canyon's mysteries, some researchers are looking to new methods of dating.
"There's only a couple of really fruitful avenues that can give us new information," Scarborough said. "Number one is the whole business of how to use fission tracking dating to define uplifting or onloading. Another method is cosmogenic dating or cosmic-ray exposure dating, which tells us how long a particular rock has been sitting at the surface."
Kris McDougall, a research micropaleontologist for the U.S. Geological Survey in Flagstaff, Ariz., has carried out more traditional dating of the lower Colorado. She presented her findings at the June symposium.
McDougall studied benthic formanifera in California's Imperial Valley and the Gulf of California, tracing marine incursions of the Gulf beginning about 12 million years ago in the mid-Miocene.
"The evidence I have found shows there were several (incursions)," she said. "The last marine incursion was about five million years ago when the rifting began in the Gulf of California."
Marine fossils are present there from 4.8-4.3 million years ago, but at 4.3 million years the Colorado River enters the Valley area and begins washing the fossils away, she said.
If that Colorado cut the Grand Canyon, the Canyon could be very young indeed, McDougall noted.
"One of the future avenues of research for me is to look at El Niño-La Niña effects," she said. "If it was dry (in the earlier period), people don't need to worry about the river flowing. If it was wet, they have some explaining to do."
Resolution of the Grand Canyon mystery may involve many contributions from many disciplines to explain the natural wonder we see today. Jill Savage described her master's project as a study of landslides in the Canyon, primarily in the Deer Creek and Surprise Valley areas.
"These slides have reorganized not only the Colorado River but also the whole drainage area," she said. "As you travel down the river you can see what impact these landslides have had on the Grand Canyon. In general, mass wasting attributes to a large percentage of the Canyon's growth."
With John Warme of the Colorado School of Mines, Huntoon will be co-leader of AAPG's Geotour "Grand Canyon Geology via the Colorado River," Aug. 6-14. He took part in a similar tour last year and said he found it refreshing to meet "young people who are challenging the traditional ideas. And, they've got the energy to have you running all over the outcrops."
As the recent symposium showed, the Canyon investigation involves contradiction and controversy, washed away or hidden geological evidence, conflicting theories, disputes and debates.
For the geologists involved, it's obviously as much fun as it can be.
"That was really an exciting meeting," Scarborough said. "I'd never been to a meeting like this where everybody who knows about a particular problem sits down together more or less in one room and tries to hash it out.
"It wasn't your typical scientific gathering."