 Grays Harbor is notable as the northernmost ria on North America's Pacific Coast because it has remained free of glaciers throughout the Quaternary due to unfavorable topography and warm temperatures.It is thought that, during glacial periods of the Quaternary, the Chehalis River was a major refugium for aquatic species, as was the west coast from the Olympic Peninsula southward for plants that later formed the northern part of the Pacific temperate rainforest in formerly glaciated areas.According to the U.S. Census Bureau, the city has a total area of , of which is land and is water.