Moreover, they are strictly licensed and regulated by the National Park Service. These trips are about as safe as they can get, given the nature of river running. But make no mistake, the wilderness can be a dangerous place. You just have to be careful down there and use some common sense. Most reported injuries on river trips occur in camp or on hikes and are of the usual garden variety camping mishaps.
Nights can be warm too.
Spring and Fall are much cooler, but you can still expect temperatures in the 90's. Thunderstorms are possible anytime, but more likely in mid-summer, and the most rain falls in August. As soon as you are sure you are really committed to running the Colorado. Outfitters fill some trips years in advance. All require deposits to hold your space.