Page:Popular Science Monthly Volume 58.djvu/515

Rh the streams flowed in the wrong direction and emptied into lakes without outlets or into the desert sands.

As the party (raveled southward into Nevada, they came upon one of the largest and most interesting of the lakes of the Great Basin. Fremont says in his journal: "Beyond, a defile between I he mountains descended rapidly about 2,000 feet; and filling all the lower space was a sheet of green water some twenty miles broad. It broke upon our eyes like the ocean. The waves were curling in the breeze and their green color showed it to be a body of deep water. For a long time we sat enjoying the view. It was like a gem in the mountains which from our position seemed to enclose it almost entirely." 'Thus runs (he narrative of the first white man who ever saw this great body of water. Of its source and general relations he knew nothing, but he hoped that it had an outlet and that the stream would lead him westward to California.

Traveling southward along the eastern shore of the lake, the party came in sight of a great rock rising from it, and camped upon the shore opposite. Fremont says: "It rose according to our estimate 600 feet above the water, and from the point we viewed it, presented a pretty exact outline of the great pyramid of Cheops. This striking feature suggested a name for the lake and I called it Pyramid Lake."

The lake thus discovered and named has had an interesting geological history, and is surrounded by many remarkable scenic features. It occupies the deepest portion of the basin of a much greater lake which once covered much of northwestern Nevada. This extinct lake has been named Lahonton, after an early French explorer.

It must be understood that the Great Basin, as its name signifies, is an extensive region with no outlet to the ocean. It is made up of innumerable faulted crust blocks, the elevated ones giving rise to the north and south ranges of mountains and the depressed ones to the desert basins lying between. Each local basin or valley has its own watershed limited by the mountains which surround it, but if for any cause the water supply from these mountains is in excess of the evaporation in the valley, a lake results, and if the supply is sufficient the lake will overflow its own basin and spread into the adjoining basins, rising to a height at which the water lost by evaporation exactly balances the inflow.

In this manner it was that the great Lake Lahonton spread over the valleys of northwestern Nevada during the glacial period. The Walker, Carson and Truckee rivers, with many smaller ones, all heading in the glacier-covered Sierras, were supplied with a great amount of water during the heavier precipitation of that period. In addition, the heat was not so great and consequently evaporation was less.

The ancient boundaries of this lake have been traced and carefully studied, and we know-that during its high-water stage it was second, in size, only to Lake Bonneville, another great lake of the same period