Nature Notes

Vol. V August 22, 1927 No. 8


Familiar features of mountain scenery are the great piles of broken rock, familiarly called "rock slides". Geologists have other names for these slides. In England they are spoken of as "scree". In America the term commonly used is "talus".

Rock slide, talus, or scree, the mode of formation is simply stated. From the face of every cliff, rock fragments are constantly falling. These are dislodged by the freezing and thawing of water in crevices, and by the wedging action of plant roots. Some are no doubt knocked down by hikers, or thrown down by them. This, however, is poor mountaineering. You can never tell who may be passing beneath, and falling stone acquires the velocity and destructive energy of a cannon-ball.

The fallen fragments pile up at the base of the cliff. There is usually a rough sorting of the fragments. The largest and roundest pieces roll farthest. The smallest and most angular pieces remain nearest the cliff. The whole pile of "scree" remains at the angle or repose. That means that the rocks are piled up at the steepest angle they can possibly assume. The ambitious hiker finds that his weight is enough to disturb this repose, and reports that he slid back two steps for each step up. The angle of rock slides is usually less than it looks. Contractors know that a rock fill will not stand "one to one" or forty-five degrees. Thirty or thirty-five degrees is a steep angle for rock slides.

"Scree" is of all sizes. The famous boulder field of Long's Peak in Colorado is full of boulders the size of a cottage. Some Rainier rock slides, of volcanic fragments, are sand-like, with an unbeatable propensity for filling one's shoes with minute, sharp-edged grains. Mountain climbers generally prefer to climb over the big boulder slopes, and descend over the smaller material. One can even slide on some scree slopes, as on a snow bank, but it takes more than "tin" pants to stand the strain.

Despite the danger from falling rocks, and a constant, slow shifting of the slide, many plants and animals make their homes in rock slides. A characteristic habitant is the vine-maple, whose tough, springy trunk will bear much bombardment. A maple or alder covered rock slide is an impenetrable thicket of slippery, yielding trees.

Two animals invariably make their homes in rock slides. These are the hoary marmot and the cony. In their rocky dens they are safe from birds of prey, and most animal enemies. Only the weasel, with his long, serpentine body, can reach the cony in the depths of his castle. One does not need to travel far from Paradise Park to see these rock slides and their interesting inhabitants. The old road above Narada Falls crossed and recrossed such a slope. The constant shifting of the loose rock was one reason for the change in location. Below Sluiskin Falls is a big rock slide, densely populated with marmots, the young of which are very much in evidence at this time, as they sit up and whistle and emulate their elders. Panorama Point, a great cliff, has beneath an imposing pile of "scree". The Tatoosh Range abounds in them.

By S. B. Jones, Ranger-Naturalist.

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