[2] The Puget Sound region was formed by the collision and attachment of many terranes ("microcontinents") to the North American plate between about 50 to 10 million years ago.

[3] About 15,000 years ago during the Vashon Glaciation, the Puget Sound region was covered by a lobe of the Cordilleran ice sheet.

After arriving along the Oregon Trail, many settlers wandered north to what is now Washington and settled the Puget Sound area.

In 1888 the Northern Pacific railroad line reached Puget Sound, linking the region to eastern states.

For a long period Tacoma was noted for its large smelters where gold, silver, copper and lead ores were treated.

Seattle was the primary port for trade with Alaska and the rest of the country and for a time possessed a large shipbuilding industry.

The driest part of the region is in the rain shadow of the Olympic Mountains around Sequim and Whidbey Island, receiving 40-75 cm of precipitation per year.

The wettest part is in the foothills of both the Cascade and the Olympic Mts, and on the west side of the Sound, receiving 125-1000+ cm of precipitation per year.

[13][14]North Pacific Oak Woodland is one of the principal plant associations of the Puget Trough, where many of the soils are well drained mesic.