Puget Sound, with its numerous channels and branches, was created primarily by glaciers. About 20,000 years ago, a glacier from present-day Canada advanced over the area, covering it in thick ice. Over the next 7,000 years, glaciers advanced and retreated several times. When they finally withdrew, they left behind many deeply gouged channels and thick layers of mud, sand, and gravel deposited by meltwater. Waves and weather have since reworked the deposits, molding landforms and shoreline, and forming beaches, bluffs, spits, and other sedimentary features.
In 1792, the British sea captain George Vancouver (1757–98) became the first European to explore the area we now know as Puget Sound, as commander of the ship Discovery. He gave names to some 75 islands, mountains, and waterways in the area, and the city of Vancouver, Washington, was subsequently named after him. Vancouver named Puget Sound after a Lieutenant Puget, who took the first party ashore to explore its southern end.