I worked several summers in the park in the early 70's working for the park service. It ain't what it used to be. But back in the day, if we wanted to truly disappear, we'd hike in above Tower Falls and scale down to the river to fish. As I recall, a very strenuous hike in and out, but the rest of the world pretty much evaporated. In 5 years and several hikes down there, I saw one person. The Black Canyon was never quite as good and usually included hikers. Heavily weighted stone fly nymphs, muddler minnows and if you are really lucky, a stonefly hatch occurs. You can also access the canyon directly below the Grand Canyon portion further upstream. Again, at least back then, you could expect isolation. Good luck and enjoy! MM