Mount St.Helens: Plains of Abraham is a 13.6 mile out and back trail located near Stevenson, WA and is rated as moderate. The trail is primarily used for mountain biking and is accessible from June until November.
I did this ride years ago and it was the most difficult Mtn. bike ride I had done to that point. The loose volcanic material was really challenging, and some of the sheer cliff faces the trail goes along were a little daunting.
We started down by Ape caves and rode up to Windy Ridge and back again. We were the only ones on the mountain that day and it was a gorgeous day and ride.
I rode this twice. Once from Windy ridge (Rough route with stairs and steeps) and once from Ape Canyon (switch back climbings). both times it was beautiful. the Pumice stone can get thick in small patches making it like riding in thick gravel. it also puts off some glare so bring sunscreen & shades. The trail it sometimes hard to see but look ahead for the stacked stone markers. the views are awesome and you can see Mt Hood and Rainer. It interesting to see how things are coming back after the Blast. Wild flowers lined the trail. it on my list of Favorites.