The Mariana Trench The deepest part of the ocean, the Mariana Trench, is deeper than Mount Everest is tall. If you placed Everest at the bottom of the trench, its peak would still be over a mile underwater. Location and Formation: The Mariana Trench is located in the western Pacific Ocean, east of the Mariana Islands, and southwest of Guam. It's a crescent-shaped trench stretching for about 1,580 miles (2,550 kilometers) and has an average width of 43 miles (69 kilometers). The trench was formed