Genesis 7:18
"The traditional explanation for the formation of Grand Canyon is that the Colorado River carved it out over the course of millions of years. A weakness of this theory is that the Colorado would have had to flow uphill over the Kaibab Upwarp, and our experience with rivers is that they tend to flow downhill, following the course of least resistance.
Current creationist thinking about the formation of Grand Canyon is that it was formed catastrophically, in a very short period of time, by water from several massive inland lakes combining to breach a weak point in the Kaibab Upwarp and scour out the canyon. This probably occurred not during the Genesis Flood but within the first few centuries thereafter.
This fits with the larger creationist model, which holds that rapid tectonic activity during the later stages of the Genesis Flood, particularly the formation of new seafloor, warmed the oceans, leading to much greater oceanic evaporation and hence much greater precipitation.
The rapid tectonic activity also ejected aerosols, dust, and ash into the atmosphere, creating the cooler summer conditions necessary for the build up of glaciers during a post-Flood Ice Age.
Creationists point to these large historic lakes in the area—including Hopi Lake and Canyonlands Lake—to provide the water needed to scour out Grand Canyon.
Today, these areas are dry and arid, but during the first few centuries after the Flood these areas saw much greater precipitation. Just as in northern climes, glaciers built up during a post-Flood Ice Age, so these inland lakes continued to fill until they broke through their natural dams and barriers, and carved out Grand Canyon." DavidRead/F7