Post 01708
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Now that the hard grinding sculpture work of the glacial period is done, the whole bright band of Sierra rivers run clear all the year, except when the snow is melting fast in the warm spring weather, and during extraordinary winter floods and the heavy thunderstorms of summer called cloud-bursts. Even then they are not muddy above the foothill mining region, unless the moraines have been loosened and the vegetation destroyed by sheep; for the rocks of the upper basins are clean, and the most able streams find but little to carry save the spoils of the forests,—trees, branches, flakes of bark, cones, leaves, pollen dust, etc.,—with scales of mica, sand grains, and boulders, which are rolled along the bottom of the steep parts of the main channels. Short sections of a few of the highest tributaries heading in glaciers are of course turbid with finely ground rock mud, but this is dropped in the first lakes they enter.
On the northern part of the range, mantled with porous fissured volcanic rocks, the fountain waters sink and flow below the surface for considerable distances, groping their way in the dark like the draining streams of glaciers, and at last bursting forth in big generous springs, filtered and cool and exquisitely clear. Some of the largest look like lakes, their waters welling straight up from the bottom of deep rock basins in quiet massive volume giving rise to young rivers. Others issue from horizontal clefts in sheer bluffs, with loud tumultuous roaring that may be heard half a mile or more. Magnificent examples of these great northern spring fountains, twenty or thirty feet deep and ten to nearly a hundred yards wide, abound on the main branches of the Feather, Pitt, McCloud, and Fall rivers.
The springs of the Yosemite Park, and the high Sierra in general, though many times more numerous, are comparatively small, oozing from moraines and snowbanks in thin, flat irregular currents which remain on the surface or near it, the rocks of the south half of the range being mostly flawless impervious granite; and since granite is but slightly soluble, the streams are particularly pure. Nevertheless, though they are all clear, and in the upper and main central forest regions delightfully lively and cool, they vary somewhat in color and taste as well as temperature, on account of differences, however slight, in exposure, and in the rocks and vegetation with which they come in contact. Some are more exposed than others to winds and sunshine in their falls and thin plumelike cascades; the amount of dashing, mixing, and airing the waters of each receive varies considerably; and there is always more or less variety in the kind and quantity of the vegetation they flow through, and in the time they lie in shady or sunny lakes and bogs.