Forest Roads and Offroads
The US Forest Service has hundreds of miles of roads suitable for recumbent trikes in Western Washington, and Mt Rainier National Park has four gravel/dirt roads, two of which are closed to motor vehicles.  The Washington Deparment of Natural Resources also has good riding roads, and King County maintains several non-motorized roads.

The National Forests also have a huge network of trails, some suitable for trikes, some too narrow or steep.  Trails in the national parks are off-limits to cycling.  Some of the best triking trails in King County are in the designated Natural Areas.  Others are undeveloped sections of multi-use trails.

It is surprising to many the places a properly equipped recumbent trike can go.  The primary requirements are fat tires, including a knobby in the back for traction; and low gearing (under 10 g.i.), which can be achieved with an internally geared hub, or a very small chain ring up front and large cog on the rear cassette.  The red Catarike Road has an 18-tooth Mountain Tamer chainring and a 36 tooth rear cog.  The ActionBent also has the same setup plus a Dual Drive hub.