This forerunner of the Great Salt Lake has left striking testimony to its old levels in prominent strandlines, not only around the margins of the basin but also on a number of central islands. It formed during a cooler, wetter climatic phase its maximum covered 50000 km2 and reached a depth of 330 m. The total mass of the water was 9×10^12 tones, a large proportion of which was abruptly evacuated when a natural dam at Red Rock Pass was breached in a catastrophic event, probably some 16000 years ago.