So that’s what those double diamonds  on the trail map mean! I had never seen this before today. In the midst of a mildly grueling (my choice, there are miles of mellower bike/hike trails as well) I discovered the Yer Mom trail today. Shout out to the parks people who maintain these awesome trails!
Hornby trail map at TrailForks.com.
Mount Geoffrey Recreation Trails brochure (pdf).
Another trail brochure (pdf).