Since I wasn't a hammocker yet, I wasn't looking for suitable trees to hang, just shade to get out of the furnace of the inner canyon. This ranges from cottonwood trees to tamarisk bushes. Yes, there are trees at Bright Angel, Indian Gardens, and Cottonwood campgrounds. It sounds like it depends on who you ask and who you are dealing with at the moment, but there's no guarantee that you would get the correct site with suitable trees. The corridor trails are byfar the heaviest travelled and May is a prime hiking month, just before the temperatures go crazy. I would say you need to be prepared to sleep on the ground most of the time. Don't let that stop you. It's a trip of a lifetime. Get you permit on Jan 1.
We are now ready to start our way down the Great Unknown.We are three quarters of a mile in the depth of the earth.We have an unknown distance yet to run, an unknow river yet to explore.What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not. Ah, well! We may conjecture many things. The men talk as cheerfully as ever; jests are bandied about freely this morning; but to me the cheer is somber and the jests are ghastly. Powell 1869