During the Pleistocene and into the Holocene epochs, an alpine glacier originating from the southwest in the Stuart Range made its way to where the town is today. Leavenworth sits on the terminal moraine of that glacier and has many glacial erratics that originated 20 miles up the Icicle Valley near Mount Stuart.
The northeasterly growth of Semiahmoo Spit indicates that sediment eroded from Birch Point has been transported by littoral drift northward, leading to the growth of the spit.