This idea of this country is as old as the time of its first colonization by white settlers. It is mostly made up of Oregon, Washington and British Columbia, along with parts of the surrounding states. At the time, the idea of an America stretching from coast to coast was too strong for any Pacific Republic; indeed, it was too strong for the First Nations who already lived there.
The area is very distinct. The mountain range, Cascades, runs parallel with the coast, enclosing a unique ecosystem of lush forest and rich soils, stretching from the Bay Area all the way to Alaska.
There is also a different culture in Cascadia that is conscious of its variance from the typical American hegemonies. A spirit for freedom and a political liberalism has often spawned many movements for something like an independent Cascadia. But it seems unlikely to happen. Which is a shame – I think this country should exist…