Wallowa River Loop
Awesome loop trail in the Eagle Cap Wilderness area with beautiful high mountain lakes. You will usually encounter a couple backpackers, but after the first eight miles it is mostly solitary running. Great loop for single female trail runners because it isn't overly used, but you do usually encounter a few other people which can be helpful if you are apprehensive about getting out there solo!
https://www.alltrails.com/trail/us/oregon/wallowa-river-loop-trail?u=i