Page:Popular Science Monthly Volume 52.djvu/636

616 beautiful lakes that now exist there, flowed far out upon the volcanic mesa at the foot of the scarp, which here has very nearly obliterated the latter feature. The moraines are apparent for a number of miles, but just how far they extend has not yet been determined. This ice stream was probably the largest of any which issued from the mountains, a fact due in great part to the elevation of the mouth of the canon. Lakes fill all the depression in the bed of this ancient glacier, illustrating how much the present scenic features of the Sierras are due to ice action. As we go south from the head of Owen's River into the valley of the same name it is apparent that only at its northern end did the glaciers reach as low as the



mouths of the cañons and flow out upon the débris cone. Opposite the highest and most rugged portion of the Sierras in the lower part of Owen's Valley, it is evident that the temperature was too high to permit the glaciers to reach an elevation as low as the valley floor. The size and symmetry of many of the moraines reaching into the valleys in the region of Mono Lake strike the attention at once. The Green Creek glacier in particular left morainal walls of great size and regularity. At the mouth of the canon the flat valley is about half a mile wide, with steep and even walls of bowlders and gravel rising three hundred to four hundred feet.