From Flagstaff, travel north on Hwy. 89. Then go west on Hwy. 64 at the junction. Go to south rim of Grand Canyon. Mather Point is a short hike from the visitor's center parking lot.
My plan was to spend the day in Sedona. When I saw the clouds forming, and moving in a northerly direction, I packed everything up and headed for Mather Point, in anticipation of a dramatic sunset. Drama is exactly what I got.