The Wikidata entry does not indicate this island is part of the Snohomish River. Look up other islands and determine how a river is specified in Wikidata, and then update the record to indicate the Snohomish River.
19,000 years ago marks the approximate time when glaciers crossed the present-day Canada–United States border into Western Washington, which is generally considered to be the beginning of the Vashon Glaciation.
