Slippery Rock - where is it?

I have talked to several people who have described a place they both called "Slippery Rock". Where is this place and how do I get there?

From the descriptions I've heard it sounds like it is somewhere near Spicer reservoir on a 4-wheel drive trail. It must be on the Stanislas river and is described as a large granite rock where the river flows over the granite and you can slide down into a pool.