greatly to its interest. The oldest lavas in the region seem to have been rhyolites and andesites, then followed basic andesites and basalts, and last of all the acid and glassy rhyolites of the Mono craters.
On the north side of the lake the tufas, built up by springs issuing from beneath the water, form a most interesting study. Great masses of calcareous material have been formed about the orifices
Obsidian Flow South of Mono Lake.
of these mineral springs, assuming odd and striking shapes. In the desiccated lakes of the desert in southern Inyo County these calcareous tufa deposits stand out in all their proportions.
It is probable that the forces producing the recent volcanic action are but slumbering, and that in the future, as in the past, movements will continue to take place along this great fault line bounding the Sierra Nevadas on the east. When the strain becomes too great, earthquakes will be felt and possibly followed by eruptions of lava.
The most severe earthquake of which we have any record on the Pacific coast of the United States was due to movement along this, fault. On March 26, 1872, nearly the whole of California and Nevada was violently shaken. The loss of life was, however, confined to Owen's Valley. At Lone Pine, near the foot of the valley,
