I know where Hanging Rock was (it's on the ICC map - just past Guy Gulch and not far before Tunnel 2), and the whole canyon side has been cut away, so it's gone. I thought I heard that Mother Grundy is still there. I may have seen it and not noticed. Where was (is) it?
Based on what I have heard and a comparison on Google Earth, I believe the formation was located directly below Inspiration Point and the old Roadmaster, at the point where the modern highway bridge now crosses Clear Creek to the East Portal of Tunnel 2. As I now live in Durango, I am reduced to Google Earth Then and Now's for C&S locations.
Here is the best lineup I could manage, pointing out the similar features in each photograph:
Denver Public Library - MCC-2344
A gentleman I met at the last DSP&P convention claims to have met the worker who blasted off the formation while widening the grade for US 6.
It would appear that only the old Roadmaster has withstood the development of the canyon.
It looks like you found the spot where it used to be.
Where was your photo of the old Roadmaster. Is that looking upgrade along the grade between the bridge at the east end of tunnel 2 and Beaver Brook?