I did the Harrison Grind today, and continued on. The actual trail name is the Campbell Lake Trail. Why then is there no cache at Campbell Lake? I took care of that oversight today.
Please start your search just up the bank a bit, maybe 3 meters off the trail, opposite side of the path from the lake. There you will find a few boulders.
You might be able to get here via quads, dirt bikes, or even 4x4's, but I don't know how. I hiked it, & I suggest you do as well. I would allow 3-4 hours return from parking. Bring some water, and expect to get a good sweat going.