Post 00221
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The main cañons are from fifty to seventy miles long, and from two to four thousand feet deep, carved in the solid flank of the range. Though rough in some places and hard to travel, they are the most delightful of roads, leading through the grandest scenery, full of life and motion, and offering most telling lessons in earth sculpture. The walls, far from being unbroken, featureless cliffs, seem like ranges of separate mountains, so deep and varied is their sculpture; rising in lordly domes, towers, round-browed outstanding headlands, and clustering spires, with dark, shadowy side cañons between. But, however wonderful in height and mass and fineness of finish, no anomalous curiosities are presented, no “freaks of nature.” All stand related in delicate rhythm, a grand glacial rock song.
Among the interesting and influential of the secondary features of cañon scenery are the great avalanche taluses, that lean against the walls at intervals of a mile or two. In the middle Yosemite region they are usually from three to five hundred feet high, and are made up of huge, angular, well-preserved, unshifting boulders, overgrown with gray lichens, trees shrubs, and delicate flowering plants. Some of the largest of the boulders are forty or fifty feet cube, weighing from five to ten thousand tons; and where the cleavage joints of the granite are exceptionally wide apart a few blocks may be found nearly a hundred feet in diameter. These wonderful boulder piles are distributed throughout all the cañons of the range, completely choking them in some of the narrower portions, and no mountaineer will be likely to forget the savage roughness of the roads they make. Even the swift, overbearing rivers, accustomed to sweep everything out of their way, are in some places bridled and held in check by them. Foaming, roaring, in glorious majesty of flood, rushing off long rumbling trains of ponderous blocks without apparent effort, they are not able to move the largest, which, withstanding all assaults for centuries, are left at rest in the channels like islands, with gardens on their tops, fringed with foam below, with flowers above.
On some points concerning the origin of these taluses I was long in doubt. Plainly enough they were derived from the cliffs above them, the size of each talus being approximately measured by a scar on the wall, the rough angular surface of which contrasts with the rounded, glaciated, unfractured parts. I saw also that, instead of being slowly accumulated material, weathered off, boulder by boulder, in the ordinary way, almost every talus had been formed suddenly, in a single avalanche, and had not been increased in size during the last three or four centuries; for trees three or four hundred years old were growing on them, some standing at the top close to the wall, without a bruise or broken branch, showing that scarcely a single boulder had fallen among them since they were planted. Furthermore, all the taluses throughout the range seemed, by the trees and lichens growing on them, to be of the same age. All the phenomena pointed straight to a grand ancient earthquake. But I left the question open for years, and went on from cañon to cañon, observing again and again; measuring the heights of taluses throughout the range on both flanks, and the variations in the angles of their surface slopes; studying the way their boulders were assorted and related and brought to rest, and the cleavage joints of the cliffs from whence they were derived, cautious about making up my mind. Only after I had seen one made did all doubt as to their formation vanish.