The Grand Canyon is a natural wonder that is truly immense in size and is one of the most world famous tourist attractions in the United States. One of the first questions they ask is How Deep Is The Grand Canyon? Many people who have been there are truly awe struck. They are amazed at its dimensions. At a length of 277 miles it stretches from Arizona right up to the state of Colorado, is 18 miles across at the widest point and a staggering 1 mile deep. Millions of years of erosion by the Colorado River and its tributaries left spectacular rock outcrops and formations of various colors exposed.