I don't think Genesis has anything to say about the GC. Creationist geologists don't say that it was carved out by the flood itself, but by an ancient lake draining suddenly through the canyon.
I was addressing the questions of how the rock layers were initially deposited in the Grand Canyon, as the Flood is usually used by Creationists to explain how sedimentary layers around the globe came to be. How the canyon itself formed is a separate debate for both parties.
BTW, catastrophism is becoming more in vogue regarding the creation of large landforms - the current wisdom is that terrain such as the Channeled Scablands and the Grand Canyon of Pennsylvania (a 1,000 foot deep gorge) were formed very quickly from the rupture of glacial ice dams. Geology involves both the long and slow as well as the fast and furious.