This trail's at the top dead-end of Stanyan, a short distance above the Stanyan trailhead for the lower Historic Trail. Upper Stanyan's steep, with sidewalk steps on both sides (pics 1 through 4).
Turning right at Belgrave & Stanyan will take you to a trailhead with old wood posts and a few steps into the forest (pic 5); no trailmarkers at either end. It's steep; you don't want "challenging," bypass this one. Last time I was there, a guy was walking his bike up.
Another trail can be seen here, an offshoot from this one, that veers to the right just behind upper Stanyan homes but then climbs so you're not overly close to their backyards. This was recommended by a fellow hiker a while back and twice trekked by me. But this is rougher than the main one and difficult to follow at times. It does, however, exit partway along the lower Historic Trail. Might this be a possible future trail extension to connect with the LH from the Belgrave trailhead?
But I digress. Partway up the main one, a treelimb across the trail is perfect as a bench. Climb over and continue up, eucalyptus aromatherapy, birdsong, and unspoiled forest surrounding you (pic 6). It zigs by the foot of a residence (pic 7) and comes out (more easily these days) at Behr & Johnstone, with a trailhead-with-marker for the delightful Fairy Gates Trail (pics 8, 9, 10) nearby. Slightly uphill from here is the Aldea Center (11th pic) and trailhead for the East Ridge Trail.
Back down to Clarendon and a block or so to the west to enter the Forest Knolls 'hood at the foot of Christopher, then onto Crestmont. Winding past Devonshire and the "Not a Through Street" signs, to descend the 355 Oakhurst Lane steps (pics 12, 13, 14, 15) to Warren, onto Locksley, and into Garden for the Environment via the short rope-railed garden stairway here. Last pic: west side of Forest Knolls and Sutro Forest.