The Bonneville Shoreline Trail (BST) follows the eastern shoreline of ancient Lake Bonneville. Lake Bonneville once filled the Great Basin which covers much of the western United States. The lake existed in the late Pleistoceine Period when what we now call Utah was a much wetter place and glaciers sat nestled in the peaks of the Wasatch Range. This ancient lake created a series of terraces or “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 Lake Bonneville shoreline is not. In the thousands of years since the lake evaporated and left its child, the Great Salt Lake, in the valley, rivers and streams running from the mountains have cut canyons and ravines across the once even Bonneville 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, at approximately 5100 feet of elevation, marks the highest level attained by ancient Lake Bonneville approximately 15,500 years ago. 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.

About 14,500 years ago, Lake Bonneville overflowed near Red Rock Pass, Idaho, causing the water level to fall some 350 feet to what is now the next lower bench (the “Provo level”). The overflow caused a flood that geologists estimate lasted up to a year.

Although the Bonneville Bench marks an ancient lake level, it does actually sit at that level today. The Bench locally occurs up to 200 feet higher than the initial 5100-foot elevation due to removal of the weight of the lake, called “isostatic crustal rebound” by geologists.

The first scientific study of the ancient Lake Bonneville terraces (shorelines) was begun in the 1870s 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 was released in 1890 as Monograph 1, one of the first publications of the newly formed U. S. Geological Survey.