Most people go during summer because that's when they take their vacation. The Canyon gets very hot then, but a little splash of river water will always be cooling. Hiking at this time is limited to shady side canyons with water. The redbud trees and many plants bloom in beautiful colors, hiking weather will be near perfect, days get long, trips often have a couple of extra days for long hikes or layovers, and it's much easier to get a reservation for a trip. Some boaters think that early June offers the best weather for a boat trip, though hiking can get hot then.
Autumn brings shorter days, along with cooler temperatures.
The Canyon quietens after mid-Sept. when all the motorized rigs have left the river. Heavy-duty rain gear with sweaters underneath can keep spring and autumn boaters warm during cool spells. This last section, beginning at Diamond Creek, offers beautiful Canyon scenery and some rapids. You can get on a trip here much more easily than in the upper Canyon, either with Hualapai River Runners or on your own. River runners will need to pay for a Hualapai permit to use the Diamond Creek Road and launch.