On August 13, about eleven o'clock in the morning, a sudden roar and a trembling of the foundation of Yavapai Observation Station on the South Rim advertised the presence of a rock slide below. A few seconds later dust began rising in vast quantities on the Canyon side of the station, first white then changing with astonishing rapidity to cream color and then red. For about a minute and a half the Canyon was almost completely obscured by the rising cloud of dust. Gradually, however, the air became clear again, but a heavy layer of dust over the glass cases and chairs in the station remained as witness to the event.
An examination of the walls beneath the station revealed that a column of rock approximately 150 feet high, 20 feet wide, and 6 feet thick had collapsed in the lower half of the Coconino formation.
The entire display was very spectacular while it lasted, and produced an extreme case of "nerves" among many of the Yavapai visitors who were present.
A VIEW OF THE ROCK SLIDE (SHOWN BELOW ARROW) AS SEEN FROM THE NORTH RIM. THE DUST CLOUD IS ABOUT 2,000 FEET HIGH.
The rock slide herein described was also observed from Bright Angel Point on the north rim; directly across the Canyon from Yavapai Station, much to the interest of a group of people on a Nature Walk. No sound of the break was heard. The first warning of the phenomenon was a large spherical mass of white "smoke", similar to that made by an explosion of a great quantity of dynamite at the top of the Hermit Shale. As the cloud slowly disseminated its color changed to a cream and then pink. The change of color was undoubtedly due to the rock mass striking the red Hermit Shale and Breaking off particles of the shale.
The interesting feature concerning the cloud of dust was that it rose out of the Canyon instead of dropping into it. This was doubtlessly due to a strong up-draft which is frequently common along the Canyon walls. After all dust had cleared out, some fifteen or twenty minutes later, the particles of Coconino sandstone were seen to be strewn over the Supai formation below. The scar left by the slide appeared like a huge waterfall on the face of the Coconino sandstone and over half the thickness of the Hermit shale was covered by Coconino talus.
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