The Wasatch Mountains extend from Collinston on the north to Nephi on the south, a distance of 150 miles. The Wasatch fault borders the west face of the range. North of Salt Lake City the fault scarp has been uncovered by the removal of sediments of comparatively late origin. In some places there are indications of recent movement on the fault; moreover, at some time within the past 500 years there has been a single abrupt movement of about sixty feet. The resultant earthquake must have been more severe than any recorded in historic time. Scattered along the entire length of the fault are warm mineral springs that bubble up to form steaming surface pools.
The latest chapter in the history of the earth began sixty million years ago with the advent of Cenozoic time. The Cenozoic era saw the development of mammals and higher plants, and, much later, the first appearance of man. In Utah, rock formations of this age are represented in the fresh-water deposits of Bryce Canyon and Cedar Breaks, in the sediments of streams and lakes, in the Wasatch conglomerate, in glacial debris, and in numerous lava flows.
In early Cenozoic time there were violent volcanic eruptions, resulting in deposition just north of the Salt Lake City boundary, near the State Capitol. About the same time there were intrusions of molten material in Big Cottonwood Canyon and near Park City, Bingham, and Alta. These masses cooled, and their mineral-bearing solutions formed valuable ore deposits. Numerous cinder cones preserve the record of volcanic activity near Zion and Bryce canyons. Lava beds, comparatively new in geologic history, cover portions of southern Utah, and there are several extinct volcanoes in this region. Outstanding among these is a crater twelve miles west of Fillmore and several perfect volcanic cones with lava flows extending from them.
The long period of intermittent disturbances which marked the upper Cenozoic era determined many of the present topographic features of Utah. In what is now the Great Basin, block faulting gave rise to a series of north-south ranges; in northeastern Utah a single great fold already in existence was cut off by faulting to produce the Uinta Mountains. In the south, igneous intrusions lifted the strata into domes, and erosion weathered away the overlying rocks to develop the Henry and La Sal ranges.
Among the geologic phenomena of late Cenozoic times in the Great Basin, perhaps most interesting to the layman is the evidence that an ancient lake once covered the greater part of Utah and extended into Idaho and Nevada. This huge body of water, known to geologists as Lake Bonneville, is thought to have originated during the last ice age, more than fifty thousand years ago, and to have endured for about twenty-five thousand years. At its maximum the lake was 1,050 feet deep, 145 miles wide, and 346 miles long. Rolling hills, abrupt cliffs, and water-filled canyons formed an irregular shore line, and low mountains rising above the water studded the surface with islands. Contemporaneous with Lake Bonneville were more than seventy smaller lakes, which occupied minor depressions in the Great Basin.
Pre-Bonneville time was characterized by alternating lakes and deserts. The lake which immediately preceded Bonneville was probably little more than a brine pond in the midst of a vast wasteland. With the beginning of Bonneville time, however, the climate began to change. Cold wet years were more frequent, and evaporation was reduced. The level of the lake rose with the wet years, and though intermittent periods of drought prevented a constant rise, the trend was always upward. Approximately 1,000 feet above the present surface of Great Salt Lake the waters came to a halt and for a long time remained stationary. Pounding incessantly against their enclosing shores, the waves eventually carved out a shelf, in some places 1,500 feet wide. This shelf, known as the Bonneville Terrace, is today plainly visible on the north face of the Traverse Mountain about 18 miles south of Salt Lake City. It appears also on the north slope of the Oquirrh Range not far from Saltair, on Antelope Island, and on the mountains near Wendover.