Joe Bartels description of the hike (Superstition Ridgeline) describes this section with this sentance:
Between Monument Canyon and Hog Canyon fanning down below to your right is another canyon (I'm not sure of the name) coming up to this indent in the ridge.
So maybe it's that "other canyon" because AZLOt 69 describes Monument Canyon's location like this:
Monument Canyon lies at the Southwest corner of the Superstitions directly beneath the southern side of the Flatiron.
Which seems to indicate that you could see Monument Canyon from Flatiron. That wasn't the case. I know it's way out there to post a pic of a canyon in Arizona and ask what it is, there are a bazillion of them, but this one seems singular.
All men dream but not equally. Those who dream by night, in the dusty recesses of their minds awake in the day to find it is vanity. The dreamers of the day are dangerous men, for they may act their dreams with open eyes and make them reality.