To the human observer, the ocean is oddly two dimensional, a stark horizon separating the sky from the reflecting, undulating water. What we don't see is the continuation of a landscape that extends completely beneath both the horizon and the water and which has all the complex surface features of mountains, valleys, plains and plateaus that are found on land.

The underwater landscape is a continuation of coastal landforms, shaped by coastal geologic processes. Much of it is covered with sediment that has been carried into the ocean by glaciers, wind or water. Olympic Coast National Marine Sanctuary contains three major submarine canyons, the Nitinat, Juan de Fuca and Quinault canyons.