RB: The GC is just sedimentary rock anyways.
Me: Negative - there are igneous intrusions at the GC seen at the bottom of the canyon.
RB: Rock type is irrelevant. The processes are the same except for very hard or very soft.
So...it's irrelevantif formed through erosion of harder rocks into layers of softer material or if it formed through the volcanic eruption of magma onto the surface. Yeah - that sounds like the same processes to me.