The trail follows the eastern shoreline of ancient Lake Bonneville. Lake Bonneville filled the Great Basin which covers much of the western United States. The lake existed in the late pleisteine period when Utah was a much wetter place and glaciers sat nestled in the peaks of the Wasatch Range. The Lake created a series of benches as it slowly receded into the desert over thousands of years. Many of Utah’s cities are built on the lower benches and the Bonneville Shoreline trail follows the upper benches.
A route around a lake shore may sound like a gentle path, but the Bonneville shoreline is not. In the thousands of years since the lake evaporated and left its child the Great Salt Lake in the valley the rivers and streams running from the mountains have cut canyons and ravines across the once even shore. The trail continuously descends into and climbs out of these obstacles along its route.
The Bonneville Shoreline Trail runs on top of the Wasatch fault for most of its route. The Wasatch fault is still active, pushing the peaks of the Wasatch Range higher. The most obvious sign of the fault is the escarped ridge faces that border much of the trail.
The Bonneville Bench is an important geologic feature of the Wasatch Front as well as one of the most striking topographic and scenic fixtures of the region. Did you know:
- The Bonneville Bench, at approximately 5100 feet elevation, is actually the preserved shoreline--called a terrace or bench by geologists--of the ice age Lake Bonneville. This shoreline marks the highest level attained by the Pleistocene lake approximately 15,500 years ago.
- About 14,500 years ago, the lake level fell catastrophically as Lake Bonneville overflowed near Red Rock Pass, Idaho. The lake level fell some 350 feet to what is now the next lower bench (the "Provo level") in a flood that geologists estimate to have lasted up to a year.
- Although the Bonneville Bench marks an old lake level, it is not level today. The bench locally occurs up to 200 feet higher than the initial 5100 ft. elevation due to removal of the weight of the lake, called "isostatic crustal rebound" by geologists.
- The first scientific study of the Lake Bonneville terraces was begun in the 1870's by Grove Karl Gilbert, a protégé of John Wesley Powell. Gilbert was a pioneer in the first geological and geographical surveys of the Colorado Plateau and Utah.
- Gilbert's classic study of Lake Bonneville terraces (shorelines) was released in 1890 as Monograph 1, one of the first publications of the newly formed U. S. Geological Survey.