Washburn, a pioneer of aerial photography, captured this view during one of 695 helicopter rides he and his team took while mapping the Grand Canyon in the 1970s. The canyon’s landscape pattern is caused by erosion on the differing horizontal layers in the sedimentary bedrock and on vertical expansion fractures that formed as the high plateau rose. These layers and fractures are visible in Zoroaster’s Throne—a pinnacle framed by vertical planes of weakness and preserved by the strength of the capping strata—and in the surrounding amphitheater, where Coconino Sandstone makes a light band of cliffs across the field of view, interrupted by shadowy alcoves in the canyon wall. Loose blocks around the base of the Throne reveal, in progress, the chipping away of cohesive rock slabs. The alcoves, amphitheater, and canyon itself are the results of this action on larger and larger scales.
Written by Tekla Harms, Professor of Geology, Amherst College
parks; rocks; mountains; cliffs; clouds
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