Probably the oldest rocks cropping out in the Rocky Mountain National Park were created over a billion years ago. The formation of the Rocky Mountains took place much later. The present landscape originated (mainly) in the last ice age (as you mention it) that ended about 15.000 years ago. Therefore the Glacier Gorge should be U-shaped (as it can be seen on the topo map) and not V-shaped.
Nevertheless the Thatchtop page is very well made. Hope to see more photos of it.