When Lisa and her posse got to the summit of the Grand, they could see Old Faithful erupting in Yellowstone Park. I used Google Earth to measure the distance between the summit of the Grand and Old Faithful, and came up with 52 air miles. This formula allows you to measure how far you can see depending on how high you are above the surrounding terrain. Using that formula, I calculate they could see about 102 miles from the summit. So well within their line of sight.