Below Supai Tunnel, switchbacks continue to the massive cliffs of Redwall Limestone, (about 3.5 miles/5.6 km) where for long stretches the trail has been blasted out of the cliff in a half tunnel. The Redwall section is awe-inspiring in every way; fantastic exposure and views mingle with a reminiscence of an age when engineering marvels were commonplace.
A hike to Roaring Springs and back is extremely strenuous and takes a full day (7-8 hours) – begin your hike before 7 a.m. Roaring Springs lies 3,050 feet / 930 m below the canyon rim and is 9.4 miles / 15 km round-trip. A day hike beyond Roaring Springs is not recommended. Many years of experience have shown that hikers who proceed beyond this point during the hottest parts of the day have a much greater probability of suffering from heat-related illness, injury, or death.
This trail is also used by mules. NOTE: Round trip to the Colorado River is 28 miles / 45 km and trail descends almost 6,000 ft. / 1,800 m. Under no circumstances should you attempt to hike from the rim to the river and back in one day! Do not hike during the hottest part of the day.
For the Complete North Kaibab Trail route description download: http://www.nps.gov/grca/planyourvisit/upload/North_Kaibab_Trail.pdf