I have the same map and know of the little trail they have marked there. However, judging from the upper stretches of Spencer being a little overgrown, I have to believe that the more informal route is no walk in the park and partially there, or non existent in spots. That being said, a great option is Spencer, West Pinto back to Rogers Trough Loop, with some road walking to connect past Montana Mountain, but this can be shortened by a little bypass route. There is a variation of this loop in the below link and the bypass to connect to Rogers Trough and shorten your connecting road walk. I did a backpacking loop so Cuff Button is included, but if you click on the route, you can focus on the loop involving Spencer Spring Trail, Rogers Trough and West Pinto.