Fig. 19 gives some idea of a part of the view from the edge of the mesa, and Fig. 20 the appearance of two of these volcanic necks. But besides high volcanic mountains such as the San Francisco Mountains and Mt. Taylor, there are, in different parts of the United States, to be found fragments of huge craters from which, in the geological past, immense quantities of lava have escaped. In some instances these craters are but fragments of huge craters, that, like the crater of Mt. Somma, in Vesuvius, have been nearly completely blown away by some unrecorded explosion during the far past. [Illustration: FIG. 19. PANORAMA FROM THE MESA AT THE EDGE OF MT. TAYLOR _From U. S. Geological Survey_] A crater of this type, known as Ice Springs Crater, is situated in the desert valley west of the Wahsatch Mountains, some 125 miles south of Salt Lake City, Utah. This crater is especially interesting from the fact that it occupies a position on a plain that was formed by the deposition of sediment in an immense lake that covered this part of the United States very long before man lived on the earth. We are alluding to Lake Bonneville, a lake that existed in a geological time known as the Glacial Epoch. This lake occupied the territory now filled by the Great Salt Lake of Utah, but towards the close of the Glacial Epoch it was immensely larger than it is now. This can be shown not only by the presence of shore lines, that are clearly marked on the sides of the surrounding mountains, but also by the ancient lake beaches, and deltas, that are common in the district, so that instead of there being the comparatively limited area of Great Salt Lake as marked on the maps of to-day there was a lake that had an area of 19,750 square miles, that covered an area on which at least 200,000 people dwell. [Illustration: FIG. 20. VOLCANIC NECKS, EDGE OF MESA AT MT. TAYLOR _From U. S. Geological Survey_] A similar lake, known as Lake Lehontan, existed at the same time, covering large areas in the western parts of Nevada. Coming now to Ice Springs Craters in Utah, we find here three small craters formed of scoriæ and lapilli (volcanic ashes consisting of small angular stony fragments). Near them lies a fragment of a much larger crater known as the Crescent. In some respects this crater was not unlike the crater of Somma that surrounded Mt. Vesuvius. It was not, however, as large, having a diameter of only 2,200 feet. From these craters streams of basalt flowed until they covered considerable areas.