Nature is the greatest of all historians. She is alike the most accurate and interesting. Her pen is the impress of time, and in characters more durable than the most lasting creations of man, she has written the story of the ages as they rolled slowly by. Impartial, unprejudiced, and in this respect omniscient, she has patiently and unerringly recorded a history more ancient than that of primeval man, more valuable than that of the proudest monarchy. And so, having in the previous chapter traced Bannock county from an unlocated spot in an unexplored desert to a settled and civilized community of fixed limits, let us now examine the scene of our story more closely, and try to read something of what Nature has written there.
The sheltered canyon mouth in which our city is built was once the bed of a huge lake, larger than many present day seas. Fish and prehistoric water animals, uncanny and awe-inspiring monsters, could we see them today, once sought their prey where now our houses raise their sheltering roofs. The benches that today are advertised as desirable building sites, were at one time the sloping shores of an inland sea. Could we but read the romance of rock and soil in all its detail, surely the most lurid fiction of man would pale by comparison.
The westernmost point of Bannock county is bounded by the Snake river, far-famed for the beauty of its valley and the rich gold deposits therein. The character of these deposits has puzzled prospectors and miners for many years, because unlike all other placer fields, it maintains a uniform fineness and coloring from mouth to source.
In the Engineering and Mining Journal for January 25, 1902, Mr. Robert Bell, a well known mining expert of this state, published an article entitled: “The Origin of the Fine Gold of Snake River.” This article was reprinted in the Pocatello Tribune, February 15, 1902, from which we quote, in part:
“One of the most plausible theories that have been suggested touching the origin of this extensive distribution of the precious metal was advanced by Captain N. L. Turner, a West Point man, who spent considerable time investigating the problem in the early eighties. Captain Turner advanced the theory that the gold was originally held in solution by the waters of a great inland sea or lake that occupied the Snake river valley subsequent to the Miocene period and that the gradual and repeated evaporation of this great body of water by subsequent lava flows resulted in the precipitation of its metallic contents, generally and evenly over its basin area. This theory would seem to account for the uniform size and quality of the golden colors so generally disseminated throughout the enormous acreage of fine gravel beds through which the Snake river now courses.
“The geological record of the rocks left along the borders of this stream offer conclusive evidence of a landlocked body of water. This great body of water, which might aptly be called Lake Idaho, was created by the closing of the lower valley by a great dam of brown Columbia lava, 6,500 feet high, now plainly exposed by erosion.”
The highest level of this lake was about 6,000 feet, and its extent 500 miles in length from Weiser to the foot of the Rocky Mountain range, and 150 miles in width. Its deepest point was over 4,000 feet.
Mr. Bell goes on to say: “This lake suffered numerous and extensive variations of level during the Tertiary period. Some of the more recent horizons are still exposed at Pocatello, where on either side of the Portneuf estuary, in plain sight from the depot, well defined benches or terraces of shore-line gravel are left exposed one hundred feet above the town; and a succession of low step-terraces of lake-shore gravel, cut by the main track of the Oregon Short Line railroad between Pocatello and American Falls, plainly indicate the rapid recession of the lake levels of this period, and its final drainage and complete obliteration by the erosion of the Snake river channel to its present level.
“Prior to the inception of the great floods of black lava that have filled the upper valley (near Pocatello), the shore lines and basin area of Lake Idaho were almost all composed of granite and Palaeozic formation. These formations were rich in placer and quartz gold.”