Growing up in Utah I could always see an old water level mark on the foothills of all the mountains. It was lake Bonneville, a huge ancient lake that covered 51,530 square miles and was over 1,000 feet deep in places.

As I explore and document I find a lot of references to the lake and I’m creating this page to link back to from those pages.

The sign at the Pilot Peak historic marker says:

Imagine Lake Bonneville some 10,000 years ago as a cast lake larger than the present Great Salt Lake. Its eastern boundary would be the Wasatch Mountains at Salt Lake City and its west boundary the Toano and Goshute Mountains to your left.

The last major glacial period in North America began about 23,000 years ago. During that time the water level of Lake Bonneville rose because of colder temperatures and a wetter climate. This freshwater lake was over 1,000 feet deep and covered 51,530 square miles – an area the size of Arkansas. If you were standing in this spot 15,000 years ago, you would be more than 500 feet underwater! Pilot Peak, the pyramid shaped mountain in front of you, was merely a small island surrounded by a freshwater lake teeming with fish.

About 15,500 years ago, water rushing through a break in a natural dam along Lake Bonneville’s northern shore dropped the lake level over 300 feet in just a few months! These raging floodwaters deepened the Snake River Canyon in Idaho. A warmer and drier climate over the next 5,000 years slowly caused the lake to shrink even further. Look carefully at the surrounding hills, especially east toward Wendover. You can still see the beach terraces left at the different high water marks as the lake receded. The Great Salt Lake is all that remains of this once vast lake.

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