Most of Davis County homes and businesses were underwater 16,000 years ago when the huge Lake Bonneville covered the left half of the state extending into Nevada and Idaho. The Shoreline Trail extending from Farmington, across the Bountiful bench to Tunnel Springs Park marks the highest level of this ancient lake when a millennia and a half of gravel, sand and silt was deposited on this shelve from waves and glacier runoff during the last ice age. Walking south from Tunnel Springs Park, evidence of an ancient lake leaving bathtub rings on the nearby hills can be seen. These horizontal striations or shelves mark levels of an ancient lake subject to seasonal runoff and evaporation. 

Reed Bitter, a geologist stands on the shoreline of ancient Lake Bonneville in Tunnel Springs. Courtesy photo

 Reed Bitter, a Bountiful resident, was a geologist by profession working decades for an oil company. He believes the bathtub rings may have been formed by one of the earlier large lakes that predate Lake Bonneville. “Lake Bonneville existed at this level right here for about 1,000 to 1,500 years and there were very strong currents in the lake that would bring down sediment and deposit it on the bench,” said Bitter. He also pointed out that the point of the mountain visible from Tunnel Springs Trail, “was formed by two currents depositing sediment” from both the Utah Valley and Salt Lake Valley sides forming a “spit.” He has seen evidence of lakes higher than Lake Bonneville up near Soda Springs, Idaho and thinks the bathtub rings were likely formed by one of these four early large lakes that occupied the large basin. He notes that sedimentary deposits mined in the Salt Lake Area give evidence of these earlier lakes. Lake Bonneville was about the size of the current Lake Michigan, and remnants of this ancient lake include Utah Lake, Sevier Lake further south and of course, the Great Salt Lake.

The Bonneville Shoreline Preserve just south of Tunnel Springs Park in North Salt Lake is a popular place for walking, running, biking and taking pictures. Especially in the spring when the grass is green and the canyon breezes are cool. The views of the islands, lake, wetlands and airport are stunning. The trails extend three miles to Ensign Peak which overlooks downtown Salt Lake City and continues 16 miles along the shore of the ancient lake to the East Bench Preserve. The Tunnel Springs park also has a large groomed grass area, playground and pavilion. The two tennis courts are also marked for playing pickleball. 

Lake Bonneville, according to the University of Idaho, was once a lake with no outlet, but started flowing over a pass at the north-eastern end in Idaho eventually causing a landslide that opened the natural dam causing one of the largest floods in the world emptying this huge lake over the course of a year leaving huge deposits of silt and boulders in its path to the Pacific Ocean. Once the lake had drained to the top of the Red Rock Pass in Idaho, it became a no-outlet, basin lake again and stayed at this Provo Level for millennia depositing the swaths of rounded gravel that is currently mined below Tunnel Springs.