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On a sheer 55-foot Navajo sandstone face, about one-third of the way up, faint lines pecked in the rock appear to dangle like an elephant's trunk and arc forward like tusks.

Bluff sculptor Joe Pachak was the first to notice that these petroglyphs west of the southeastern Utah town could depict long-extinct mammoths, and he led rock art researcher Ekkehart Malotki to the site in the early 1990s.

Although ancient rock art is notoriously difficult to interpret, Malotki has concluded the images indeed depict Columbian mammoths, chiseled into the rock when these massive pachyderms still roamed the Colorado Plateau more than 11,000 years ago.

If he's right, the images are the only known rock art in North America depicting Ice Age megafauna. Such images would be proof that paleoamericans not only shared the Colorado Plateau with these large mammals, but used them for artistic inspiration.

But many in Utah's scientific community challenge Malotki, a retired languages professor at Northern Arizona University in Flagstaff, arguing his methods lacked scientific rigor. Critics contend Malotki's study failed to fully document the site — not just the entire rock art panel but the gravel bar below it, which could have yielded valuable clues.

"This was an introductory-type study," responds Malotki's collaborator, Tucson archaeologist Henry Wallace. "There is a limit to how much study you could do. I would be really surprised if there was preserved material [in the gravel] that would give you any clue to what's on the rock face."

The case highlights the tensions over prehistoric rock art, which does not lend itself to scientific scrutiny. No techniques are available to reliably date it, and the images' meaning was lost with the passing of the preliterate people who created them. Academic archaeologists and geologists focus on artifacts and other clues that can be analyzed, leaving rock art to scholars who are typically not as well-grounded in scientific techniques.

'Tell-tale features' • For years researchers have struggled to decipher enigmatic images pecked and painted into sandstone walls by waves of prehistoric peoples who inhabited the Colorado Plateau for at least 5,000 years before the arrival of modern Indians.

Prehistoric depictions of extinct megafauna are common in Europe, but vexingly scarce in the Americas. If Malotki is right, his mammoth panel would be by far the oldest known rock art on the plateau.

He argues the petroglyphs are at least 11,000 years old, chiseled by Clovis people before mammoths and other large mammals died out. The Clovis are the cultures associated with the descendants of ancient Asians who crossed the Bering land bridge and left some of the oldest artifacts in North America, including five-inch fluted stone projectile points crafted to take down big animals.

The 72-year-old German-born linguist makes his case in the fall 2011 edition of Rock Art Research, a peer-reviewed, premier journal published by the Australian Rock Art Research Association. Malotki also will present his findings at the Utah Rock Art Research Association's annual symposium Sept. 24 in Price.

"The mammoth has anatomically diagnostic features, a trunk and tusks. They have tell-tale features that make for easy identification," said Malotki, who has published three photography books on Southwestern rock art.

The images in question are near Sand Island, a heavily visited rock-art site and recreation area along the San Juan River. They are part of a panel that includes many disparate images, reflecting a variety of styles and periods right up to historic Ute times, according to Pachak.

Using magnifying glasses, Malotki and Wallace examined the first suspected mammoth glyph, which appears to have a bison superimposed on it. They determined that the lines were not etched with metal tools and patina had formed inside the lines, proof they are not the work of modern hands.

They photographed the panel with an auto-focus camera and artist Joe Ciaccio re-created the images with pen and paper. He discerned a second mammoth-like image several feet to the left of the initial one. Both are left-facing and contain features consistent with trunks, tusks and the mound on the back of mammoths' heads.

'All petroglyphs are controversial' • Malotki showed the drawings to David Gillette, the former Utah state paleontologist who excavated the famous Huntington mammoth skeleton, now an anchor exhibit at Price's Prehistoric Museum. According to the study, Gillette agreed the images could be Columbian mammoths and speculated the short tusks relative to the trunk indicate the artist was depicting a female or young animal.

"It is compelling evidence of the species. What is really the exciting feature is the bifurcation at the base of the trunk," Malotki said.

The trunks of Proboscidean mammals, which include elephants and their extinct brethren, have pincers at the end that are used for grasping food. An exaggerated form of these "fingers" appears on one of the glyphs.

An ancient rock artist who had never seen a mammoth or a modern forger would not have included such an anatomical detail, Malotki reasoned.

But in an interview with The Salt Lake Tribune, Gillette was not so certain.

"The problem is all petroglyphs are controversial and difficult to interpret. It's hard to accept this as concrete evidence of human and mammoth association. But it's a reasonable association because we know they were associated off the plateau in New Mexico and Arizona," said Gillette, now a research paleontologist with the Museum of Northern Arizona.

Malotki argues the 16-foot distance separating the glyphs from the ground is further evidence of their antiquity, because it suggests the ground has been eroded away over the millenniums since their creation. Bluff geologist Gene Stevenson said he cautioned Malotki against drawing such a conclusion, yet the study doesn't mention his doubts.

"Something of this historical importance requires some empirical evidence, not just the sketching of a predetermined image by a retired linguist," he said in an email. "In this case, he came to find what was already in his mind — and found it."

Stevenson now conjectures the face may not have been exposed at the time Malotki says the images were created. That's because 13,000 years ago, the river corridor may have been covered with cobbles deposited by massive runoff during a warming period when glaciers in the San Juan Mountains were melting, he argues. It would have taken several thousand years for the material to erode down and the varnish to form on the rock face bearing the petroglyphs.

Critics blast Malotki's failure to obtain a research permit from the Bureau of Land Management, required to collect or survey artifacts at archaeological sites. Rock art is a gray area, BLM archaeologist Byron Loosle said.

Wallace, a co-author on the mammoth paper, conceded they should have gotten a permit, but noted the on-site investigation was limited to a visual inspection and photography.

"I didn't take this lightly. I went up there extremely skeptical. In this case I walked away not 100 percent convinced, but in the 90s," Wallace said. "This is the best case I've seen for something like this. If someone comes along who can disprove it in a rigorous manner, that's fine with me."