Arizona republican., 1902-10-15
ANCIENT LAKE OF TONTO

an artcle by James C. Goodwin on the ancient lake of Tonto which appeared some time ago in the University Monthly:
 Lake Quiburis. an ancient Pliocene lake. as described by Professor w. P. Blake in the Arizona Monthly is of sci entihc interest; a story from geology: description of the former condition of a portion of southern Arizona.
 This nearly land-locked estuary. which was open to the sea to to the north. was elevated some four thousand feet by great epeirOgenic uplift and changed into what is now known as the San Pedro valley. At this time and during the late periods O. the territory nearly all of the mountain ranges re- ceived an addition of many thousands of feet to their height, and hundreds of theusands of square miles of land was elevated above the ocean.
 At the beginning of the tertiary era there was no Salt or Gila river At the close of this era. mountains had been formed by the epeirogenic up- lift and igneous eruptions. water shedding from these mountains filled many deep depressions. making chains Of lakes that then extended along the river valleys from their sources to where the rivers now unite
 If nature planned the river systems or Arizona, time has completed that mighty task and today not a lake ex- ists: but dry basins, small valleys and deep canyons. Their cutting through mountains teaches us the stupendous power of water as a mechanical agent.
 
 arv of these dry lakes I have ever seen is Tonto basin. It is not only interest ing from geological standpoint. but economically as we'll for this IS one Iof the many places that the people of Salt River valley hope again to sec turned into a lake or reservoir. They can hope to see it as it was at the end of the tertiary era as at that time a mountain barrier extended from the north along the Silver King range of mountains to the Mazatzal. or Four Peaks. Before the upheavel of this mountain. a great trachyte flow had covered the country for many suqare miles, and to the depth of from 800 to 1.000 feet In their formation the Sil- yer King mountains crossed this tra- chvte flow diaFonally. leaving it alto gether at the Tonto dam site at the north end. That part of the flow lying 10 the west is now known as Supersti- tiCn mountain.
 The fexure that formed the Silver King mountain was either an over thrust hexure, or the flexure faulteG along its axis, making a displacement of some two thousand feet. leaving the eastern half a great monocline. This fault is best seen south of the Silver King mine.
 The top of this monocline is covered from 5CO to 1000 feet deep with trachyte and underneath this lies 800 feet or more of limestone and below the lime stone many feet of Guartzite, all rest ing on a basic diorite. Twenty miles north at the Tonto dam-site the condi- tiOus are nearly the same: a great mon- ooline dipping to the east, but without the trachyte capping. Tn addition you find a conglomerate or puddinS-stone gtra tum from ten to fifteen feet thick underlying the quartzite and resting on the diorte.
 Since the upheavel of the Silver King mountain the Salt river has cut a can yon about 1000 feet deep. and this can von has drained the ancient lake of To7to.
 TOlto basin. as an ancient lake, then as now. was bordered on the west by the Four Peaks or Mazatzal range of mountains; on the east by the Sierra Anches mountains; on the north by low range of slate mountains and on the south by dikes and many parallel ra nges of mountains. The country ad- iacent to the Tonto basin abounded in many small lakes, but they have all been drained by the uplift and erosion.
 Alter these lakes had been filled with water. the excess began to flow over irto and fill this great basin of Tonto Thus began the formation of many "r@cl1s that now flow into this basin. The largest and longest of these dis charges flowed frCn the east and since that time it has cut through many deep barriers. turning small lakes into bas- ns. and is now known as Salt river This great lake as we'll as other smaller ones in this part of Arizona, received a great abundance of debris-forming lacrustine deposits. the washings from newly made mountain ranges. These sediments may be seen in horizontal beds of great thickness extending far up the sides of the bordering noun teins
 At the end of this ancient lake, where Salt river enters it through a box can von from the east, can be seen horizon tai beds of unconsnlidated claws, sands ond gravels over five hundred feet in thickness Time has cut deep arr0yas throueh this deposit leaving long ridges, extending from near Salt river tc the eur nit of the low mountains to the cast and south. Going from Salt river 'o Globe today you pass over one of theoe long ridges.
 This Lake Tonto was in the form cf ! rieht angle. one side extending north ward up what is now known as Tonto creek for a distance of about 24 miles and varied in width from twelve to