Yes, very legal if you stay on the original roadbed--it is all public lands under the US Forest Service. There is a private residence at Illium next to the roadbed, so stay out of their yard. The facilities at Vance Junction are also Forest Service.
Some discussion recently about the roadbed around Trout Lake. The present road is the rail right-of-way except at the trestle as the current road obviously skirts the trestle to the east on a big fill. The bridge was part of the county road system for a number of years after abandonment with just planking laid on top of the ties--no guard rails. But when the bridge started to deteriorate, it was closed to vehicular traffic and the road moved.
The current conflict appears to be winter weather is keeping the contractor from working on the bridge (it has been 24 below zero this past week in Silverton)and the Forest Service is trying to hold him to a contractural deadline that seems to ignore blizzards, intolerable working conditions, etc. I had lunch yesterday with the USFS employee who is in charge of this project, but we were discussing Red Mountain projects and just barely touched on Trout Lake.
And speaking of Red Mountain, the Red Mountain Project in conjunction with the Trust for Public Lands is working towards acquiring much of the Silverton Railway right-of-way leading into the Corkscrew Gulch turntable as well as the turntable site. Private negotiations are in progress. See
www.redmountainproject.org.