For those who continue downriver beyond Phantom Ranch, serious white water lies ahead. On most rivers, rapids are rated on an international scale, from Class I to Class V. In Grand Canyon, rapids are ranked on a scale of 1 to 10, with 1 being a small riffle and 10 the highest difficulty that is still navigable.

The severity of a rapid can fluctuate with changes in river flows (releases from Glen Canyon Dam, run-off from rainstorms), and many rapids have more than one run or route, with differences in difficulty. Granite and Hermit Rapids, at mile 93 and mile 95, respectively, are both ranked 9.

At mile 98, notorious Crystal Rapid was a mere riffle until the river channel filled with flash-flood debris in 1966. Crystal changed again in 1983 when another flood swept downriver, moving boulders and creating a 10-plus rapid with a notorious hole.

Boaters have their own lexicon to discuss the river’s white water: washing machine, cheese grater, haystack, and other colorful terms. A hole is the boat-sucking hydraulic on the downstream side of a large rock, and the hole in Crystal is said to be the canyon’s biggest, capable of trapping and recirculating even very large boats.

Past Crystal, boaters encounter the rapids known as the Gem Series—Agate, Sapphire, Turquoise, Jasper, Jade, Ruby, and Serpentine Rapids.

At mile 107, Bass Canyon enters from the southwest. The area near William Bass’s historic camp is a popular layover for river runners and backpackers. Bass built a cable crossing here to connect his two trails, the first rim-to-rim route in Grand Canyon. The Tapeats sandstone bench on river right makes a great campsite, with historic Bass Camp a couple of miles up the North Bass Trail. On river left is the abandoned Ross Wheeler, a metal boat left behind during a 1915 expedition, which can be reached by the South Bass Trail.

Just past mile 116, Royal Arch Creek enters the main canyon from the south. Elves Chasm, a magical grotto of maidenhair ferns and trickling water, is a short walk from the river, near the mouth of Royal Arch Canyon. Two straight river passages—Stephens Aisle, which runs north–south from mile 117 to mile 119; and Conquistador Aisle, heading east–west from mile 120 to mile 123—lead to Middle Granite Gorge.

Ask river runners about their favorite rock layer in Grand Canyon, and most of them will probably answer, “Tapeats sandstone.” There’s a lot of it in this section of the canyon. Blacktail Canyon, at mile 120, and Tapeats Canyon, at mile 134, are both carved from the Tapeats. This dark brown sandstone, formed about 545 million years ago, erodes into interesting platforms and ledges and often bears fossilized brachiopods, trilobites, or “worm tracks.”

The Thunder River Trail leads up Tapeats Canyon to half-mile-long Thunder River, also accessible from the North Rim. The dark mile-long section of the canyon from Helicopter Eddy to Deer Creek is known as Granite Narrows, where the canyon pinches to a width of 76 feet.