If they put in a simple dirt track bike trail through the Eel River canyon it would be a great way to explore the canyon. The trail would not need to be graded and groomed. People of all ages can ride mountain bikes. There are even electric mountain bikes now.
Enough people would use the trail that the pot growers wouldn't bother them I think, plus you'd have a ranger patrolling the trail every week or so.
Since it's clear the trains ain't coming back to the canyon, a simple, single track dirt trail would be cool. I'd like to see tracks kept intact outside the canyon for possible tourist train usage though. Eureka could have a successful Skunk Train type operation I think.