Fault Block Mountains
January 02, 2001
Thirty miles south of Salt Lake City, near the mouth of Provo Canyon in Orem, Utah is an excellent example of fault block mountains. The north-south trending Wasatch Range extends throughout the center of Utah. The western flank of the range is very steep and relatively straight, the result of displacement along the extensive and still-active Wasatch Fault. Summits along the crest of the range have elevations between 9,000 and 10,000 feet. The mountain-sized fault blocks of this region developed in a fairly orderly fashion, breaking roughly at right angles to the westward direction of stress. As visible in this photo, the truncated spurs of the Wasatch Mountains provide evidence that movement on the Wasatch fault is geologically recent. Utah lays claim to many thousands of faults, large and small. Mountains have been formed by normal faults, reverse faults, thrust faults and extension or detachment faults. The valley held an arm of Lake Bonneville, a lake that formerly covered this area 25,000 years ago in the Pleistocene era. This lake varied in level over the years and left clearly seen shorelines, benches, ridges and gravel bars. The slope on the left of this picture is an example of this ancient deposition.