Estimates of the canyon’s origins vary from under 6 million (SN: 1/25/14, p. 22) to more than 70 million years ago (SN: 1/12/13, p. 15) — old enough for dino visitors. A comparison of the Colorado Plateau’s rocky features now concludes that the older, western section of the canyon had to have been carved out much more recently than 12 million years ago.
The giveaway is the nearby Grand Wash Cliffs, researchers from Arizona State University report online June 10 in Geosphere. These cliffs formed 18 million to 12 million years ago as a fault shifted the ground. In the millions of years since then, erosion has transformed the steep cliffs into more gradual slopes. Cliffs along the western Grand Canyon are comparatively much steeper, the researchers found, suggesting that the canyon walls formed more recently than the Grand Wash Cliffs and significantly later than the big dinosaur die-off.