Lieutenant Doane's suspicion that many quiet-looking springs were slumbering geysers, was speedily and grandly justified. The very next morning his company were awakened by a fearful hissing sound, accompanied by the rush of falling water. On looking out, they saw on the other side of the stream a small crater, three feet in height, with an opening 26 inches in diameter, which had scarcely been noticed on the previous day. Now it was playing a perpendicular jet to the height of 219 feet, amid great clouds of steam, and causing the ground to tremble as the heavy body of water fell with tremendous splashes upon the shelly strata below. Huge masses of rock were torn from their places and borne away into the river channel. It played thus, steadily, for ten minutes, giving time to obtain an accurate measurement by triangulation. This crater gave no notice of being a geyser, and its appearance and size, compared with others, were altogether insignificant. "We were more than ever convinced," adds Lieutenant Doane, "that continued observation would develop the knowledge of geysers in greater numbers, and perhaps of greater projectile force than any we had seen."
Crossing the river once more to the south side--that of Old Faithful and the Castle--we find another large group of springs, the chief of which is the Giant. This is remarkable rather for its immense flow of water than for any peculiarity of structure. It has a rugged crater, shaped like the base of a broken horn, twelve feet high. Its cavity or nozzle is seven feet in diameter.
During its quiescent state the boiling water can be seen in its chambers at a depth of forty feet, the action of the steam and water together producing a loud, rumbling sound. Near, and acting in concert with it, are half a dozen smaller craters from two to eight feet in height, constantly full of water, and boiling violently from two to six feet into the air. "This great geyser," says Lieutenant Doane, "played several times while we were in the valley, on one occasion throwing constantly for over three hours a stream of water seven feet in diameter, from 90 to 200 feet perpendicularly. While playing it doubled the size of the Firehole River."