During the last Ice Age, northwest Utah was covered by a huge lake, Lake Bonneville. When the climate changed, the lake dried up, leaving a smaller lake, now called Great Salt Lake.
Bonneville Salt Flats - Thousands of years ago, Lake Bonneville covered most of Utah. After the lake dried up, what's left was miles of brilliant white salt flats, where nothing grows. Stop at the rest areas on Interstate 80, near the exit for the Bonneville Race Track, almost at the Nevada border. Climb up the little observation platforms to look out over the endless white desert, and step out onto the crunchy salt surface.
Tip: While driving on Interstate 80, there are super mirages as you're driving along. The salt flats look like a shining blue lake on either side of the road.