Columbia River Basalt Group map shows main regions of basalt exposure in Washington, Oregon, Idaho and Nevada, USA. (usgs.gov)- King County, Washington (Wikipedia)
King County is located in the U.S. state of Washington. The population was 2,269,675 in the 2020 census, making it the most populous county in Washington, and the 13th-most populous in the United States. The county seat is Seattle, also the state’s most populous city.
- Cascade Range (Wikipedia)
The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as many of those in the North Cascades, and the notable volcanoes known as the High Cascades. The small part of the range in British Columbia is referred to as the Canadian Cascades or, locally, as the Cascade Mountains. The highest peak in the range is Mount Rainier in Washington at 14,411 feet (4,392 m).