Hiking's one of the things I bought my UK Survival for. Not as cool as running shorts (which aren't suitable for hiking anyway), but the upkilt breeze is refreshing even on hot days. The pockets comfortably carry a whole bunch of everything, then I have a hydration pack for insulated water.

90+F is a bit warm for it, but it'd be too warm for anything else I'd want to wear hiking, anyway. I'm thinking of getting a Hiking SportKilt for those hot days, given that summers here are hot and dry and not terribly windy (good tip upthread).