Peter Hassrick wrote, "Geological curiosities become the signposts for civilizations on the move. When the terrain is unfamiliar, natural landmarks guide travelers across uncharted reaches, serving as beacons in the wilderness. But as the paths become worn, so do the guideposts. They soon take on the etched identity of the people who pass and inevitably reflect the human failing to record that 'Kilroy was here."'

"Register Rock in Idaho served the Oregon Trail, and Remington's depiction of it embodies the whole story of Western migration. The bewildered Indian gazes in wonderment at the scribbled initials of an intruding civilization. The cow skulls tell of the journey's hardships for animals that did not complete the journey to greener pastures. This site was the resting spot for many wagon trains; here they spent the night and cooked a meal which may well have consisted of their own oxen."