Posted: 12 Mar 2015 01:20 AM PDT
So how exactly did all of this salt get underneath the city of Detroit? About 400 million years ago, there was an area of land that is now called the Michigan Basin. This area was separated from the ocean but kept sinking lower and lower into the Earth. Because it continued to sink, the salt water from the ocean poured in as the ocean receded. Once the ocean water evaporated, it left behind huge salt deposits.