I’ve watched a volcano in Iceland fill a valley with lava in 4 months. I watched as a road was washed out and a cement bridge with a 20 foot cavern left behind in 4 hours. You can’t make me believe it took millions of years to carve out a canyon.
That rock was unconsolidated. Basically, it was sediment and not rock. Sediments need to be buried within the earth to become rock. At a minimum, about 4,000’ before the process begins. One exception are reefs which are lithified as they are created. Think about peat that forms in a swamp. It has to be buried quite a ways before it becomes coal.