Page:Popular Science Monthly Volume 52.djvu/635

Rh of the Sierras, making more marked still the great fault on its eastern side and differentiating it more completely from the region to the east. From the Mohave Desert northward, the whole length of the Sierras, these lines of weakness have given rise to an almost continuous line of volcanic craters and flows.

The Glacial period in the Sierra Nevadas was finally ushered in, being doubtless due to the increased elevation in this enormous fault block. Whether this period was contemporaneous with glaciation



in the East is not known. There are many things, however, which lead us to believe that it was more recent here. Glaciers still exist in the shadows of the higher peaks, and the facts that their scourings are so fresh and the moraines so slightly modified are strong evidences in favor of the view that the ice period terminated very recently. The glacial phenomena about Mono Lake have been studied by Le Conte and Russell, but farther south they remain still almost unknown. Owen's River heads in the Sierras about forty miles south of Mono Lake. It is a stream of considerable size, draining a large basin, and issues from its rocky gorge at an elevation of eight thousand feet, thence flowing for many miles across the elevated volcanic table-land. Because of the elevation the immense glacier, which once gathered its strength in the basins of the fifteen