Abstract

The seemingly unlikely coastal landforms and features in northern Utah area offer significant information about Lake Bonneville, the immense Late Pleistocene lake which inundated this region to varying depths from approximately 30,000 years ago to 13,000 years ago. At its maximum, Lake Bonneville was approximately 1,000 feet (305 meters) deep and covered an area of approximately 20,000 square miles (51,800 square km) in northern Utah, extreme southeastern Idaho, and extreme northeastern Nevada. The lake cycle consisted of basically three major phases: (1) a prolonged closed-basin phase predominated by transgressive stages approximately from 30,000 years ago to 16,500 years ago; (2) a brief phase of intermittently open-basin, threshold-controlled stages approximately from 16,500 years ago to 15,000 years ago; and (3) a short phase of rapidly regressive, closed-basin stages following the catastrophic Bonneville flood approximately from 15,000 years ago to 14,500 years ago.

Attempts to define the history of this great lake originally began in the mid- 1800’s with the intensive efforts of G. K. Gilbert, still recognized today as a highly respected authority on Lake Bonneville. After thorough exploration of the lake basin, his in-depth study of Lake Bonneville was published in 1890 as U.S. Geological Survey Monograph 1. Today, research continues in attempting to interpret the many varied aspects of Lake Bonneville. As it transgressed and regressed, Lake Bonneville left remnant erosional and depositional features, which today are very prominent landforms within the Bonneville basin. Relict erosional features of Lake Bonneville include shorelines left at the lake margin at various transgressive and regressive levels of the lake, sea caves found in rocky outcrops at the lake margin, and sea stacks, rocky outcrops which often record major influence of wave action. Depositional features of the lake include massive deltas, spits, barriers and tombolos; which reveal the tremendous ability of the lake to alter the local landscape. Continued research of these features will help to better interpret not only Lake Bonneville, but also the geologic, hydrologic and climatic processes of this region which collectively contributed to the formation of this great lake.