Wow, what a great trip! And kind of a clothing challenge. It聮s apt to be hot聴very hot聴in places. During the summer months the rims top out at 80 or so, but down in the canyon it can reach 120 for daytime highs. And there聮s a good chance of a thunderstorm or four or five.
The Capilene 1 T-ShirtSo my kit would include things that are comfortable in hot weather and that dry fast (from either sweat or dunks on the Colorado or from thunderstorms). My first choice for a shirt is anything made with Capilene 1, a very light, polyester-based fabric that is an ideal by-itself layer in hot weather, and a great base layer if it cools off. The women聮s T is $36, and it comes in white, which could be handy.
Add to that an Bodybit 150 L/S Atlas Zip ($65). It聮s a merino wool piece, very comfortable across a wide temp range, perfect for a base layer on cooler evenings.
I might pack some cotton, but only to wear in the evening or when you聮re done hiking for the day, otherwise it just gets too wet when sweaty, and doesn聮t dry well.
For shorts, perhaps the Backcountry Short ($45). They聮re made with a light, fast-drying Supplex nylon, and are designed for hiking, with a gusset for extra mobility and pockets for small essentials. It depends on the look you want, but a pair of tights for under the shorts when gets cooler would be fine. Patagonia聮s Capilene 1 bottoms are $36 and would make a nice match with the tops.
To sort of round out the basic clothing set, 聮s Salathe Jacket ($79) is a light fleece piece, trimly cut, that聮s not too warm. For those occasional desert showers, the Torrent Rain Jacket ($129) packs down well, has good breathability, and will keep you dry.
Good luck!
Check out all our warm-weather picks in our annual Summer Buyer’s Guide.