The topography of SeaTac is defined by the rolling Puget Sound lowlands, shaped by massive glaciers during the last ice age. The city sits on a broad plateau, generally ranging from 165 to 350 feet in elevation. Because it is situated on this plateau, it largely escapes the flood risks associated with the nearby Green River valley.
The terrain is relatively flat with gentle, rolling hills, which originally made it an ideal location for an airfield. Angle Lake sits in a depression created by a melting glacial ice block. To the west, the land begins a gradual slope downward toward the Puget Sound, while to the east it drops more steeply into the Duwamish and Green River valleys.