Access Recreation Based in Portland, Oregon, Access Recreation developed a set of guidelines for information to include in resources for disabled people.
Access Trails is their associated website with trail information for the Portland-Vancouver region.
Accessible Nature is a collection of links to reportedly wheelchair accessible or easy trails around the United States and parts of Canada. From what I can gather, it is mostly a collection of links found through internet searches, but it does cover a large area.
Accessible Adventures in the Pacific Northwest is a series of videos produced by the US Forest Service. It explores trails in Washington and Oregon.
Trail Link is the trail guide website of the Rails-to-Trails Conservancy. Many of their trails are paved. The link goes to wheelchair accessible routes.
Washington Trails Association is the largest website of trail guides in Washington. There is a very engaged community. This link goes to the ADA accessible hikes.
Washington State Parks Accessible Recreation hosts a map of ADA accessible camping, hiking, and other recreation spots in state parks.
Outdoors For All is a Seattle-based organization that leads outdoor recreation opportunities for people with disabilities.
DREAMAdaptive is a Montana-based organization providing adaptive outdoor recreation opportunities.
Wilderness Inquiry provides inclusive outdoor adventure travel for people of all backgrounds, ages, and abilities.
RAD Recreation Adaptive Society provides rentals of adaptive equipment in British Columbia, Canada.
National Parks Access Pass The National Park Service provides a free America The Beautiful pass to citizens with a permanent disability. It provides access to all national lands that charge an entrance fee and gives a 50% discount on camping and other fees. You can get a pass online by submitting a form with documentation of your disability, or you can request a pass at any ticket booth where you will have to sign an affidavit stating you have a permanent disability.
Washington State Parks Disability Pass/ Disabled Veterans Pass the disability pass provides free entrance and 50% discount on camping at all WA State Parks. You must meet the SSA definition of disability and provide proof on official letterhead and/or be receiving SSI/SSDI. The disabled veterans pass provides free entrance and free camping and other recreation fees to veterans with a service connected disability of at least 30%. Documentation is required.