By early Permian time, about 260 million years ago, what is now southwestern United States, around the Grand Canyon area today, was becoming pretty arid. The Coconino sandstone represents an extensive dune terrane, essentially a Permian desert that formed there. Wind-borne or eolian sand in dunes forms sloping dune faces, and when these are preserved in the sandstone, the sloping forms are called cross-beds, angular curving beds within a single package of sand. We can infer wind direction from the orientation of cross-beds.
The Coconino is typically a white, almost pure sandstone 60 to 100 feet thick. It is so resistant that it forms near vertical cliffs in places, and makes for some of the most difficult passages down into the Grand Canyon today. I climbed through it on a route in the western part of the canyon back in 1987 – a 70-foot section that required the use of ropes to descend.
The Coconino is extensive and forms prominent landscapes across much of southern Utah as well as northern Arizona.
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On August 15, 1950, an 8.6-magnitude earthquake in Assam, eastern India, reportedly killed more than 30,000 people, but other estimates give much smaller death tolls. This quake was definitely related to the ongoing collision between India and Eurasia, pushing up the Himalayas. There are other consequences to that collision, and this location, in northeastern India and adjacent Tibet, is essentially at the corner of the collision, so mountain belts and fault zones change direction here from about east-west to more north-south.
—Richard I. GibsonSee also The Earth Story's report on the Coconino
Photo by Richard Gibson