When an early expedition of government explorers first studied the Unaweep area around 1875, one geologist wrote in his field notes that the sheer cliff walls and interesting amalgamation of rock layers reminded him of “a miniature Yosemite.”
Even today, geologists still peer up at the canyon’s walls with wonder, as they imagine the great feats of nature that conspired to create Unaweep Canyon.
Geologists like Grand Junction’s Bill Chenowith have spent nearly a lifetime analyzing the remains of Unaweep’s geologic past. Chenowith, 84, started as a uranium geologist with the Atomic Energy Commission in 1954, and spent the next several decades studying the geology across the entirety of the Colorado Plateau. Now retired, he is still drawn back to Unaweep Canyon by its history, and continues to lead geology trips through it under the auspices of the Museum of Western Colorado.
“Unaweep is really what we call a wind gap,” Chenowith said, or “a huge canyon that has no major river flowing through it,” which explains one of the first complexities that Unaweep presents.
Although East and West creeks flow in opposite directions from the Unaweep Divide, with East Creek draining east to the Gunnison River and West Creek draining west to the Dolores River (the only canyon in the world said to do this), these two streams are too small to have carved the entirety of Unaweep Canyon. A larger river likely would have done the work to shape a canyon as deep and wide as Unaweep, but the question of which river that could be has puzzled geologists for decades.
The Colorado is an obvious choice, since it flows in the same direction through the Grand Valley just a short distance north. But no sediments diagnostic of the Colorado River have been found in Unaweep. There are deposits that point to the Gunnison River, but those exist only in the western part of the canyon.
Some geologists have theorized that the canyon wasn’t cut by a river at all, but rather by a glacier that existed in the late Paleozoic.
Researchers at Colorado Mesa University and the Grand Junction Geologic Society have spent years studying the question of what carved the canyon, theorizing that it was originally cut by the Colorado, but that at some point, the Gunnison joined the Colorado, and it was the force and strength of the combined rivers that eroded the canyon. The Colorado eventually evacuated the canyon, leaving just the Gunnison, which then abandoned Unaweep about eight million years ago.
In the midst of all the comings and goings of the regional rivers, the topography of Unaweep was also being shaped by other forces. Around 330 million years ago, the Uncompahgre Plateau began to rise. Prior to this, the area was flat and at sea level, as evidenced by the limestone deposits now seen from Glenwood to Moab. This part of the Rocky Mountain Range formed as the Uncompahgre Plateau began to rise. The process exposed truly ancient rocks – both metamorphic and igneous which the U.S. Geologic Survey has dated to be as old as 1.7 billion years, representing some of the oldest rocks in Colorado.
Over time, this mountain range was eroded down to its roots, supplying the sand, gravel and mud for the redrock formations of southwestern Colorado. This process of erosion removed over half-a-billion years’ worth of material from the rock record, creating what geologists have deemed the “Great Unconformity,” which you can see from the Divide Road turnoff along Highway 141 in Unaweep Canyon. The gap is visible where you notice a line between the granite and the newer red sandstone. This particular unconformity is considered “Great,” due to the extreme gap of 1.2 billion years, representing a quarter of the Earth’s history.
A second uplift occurred around one million years ago, causing the 7,000-foot uplift found at the Unaweep Divide, where East and West Creeks flow in opposite directions – and, in so doing, led to the naming of the canyon as Unaweep, which in Ute means “canyon with two mouths.”
“So what you see at Unaweep is really part of the roots of ancient mountains,” Chenowith explained of the dramatic and mysterious landscape of Unaweep Canyon.