I agree completely with AROTC and I have lived in the desert SW since 1958.
Try a Cabela's soft canvas trail shirt. Well made, pure cotton and good size pockets.
Pants, use some old Dockers or any number of lightweight, loose fitting cotton pants. Jeans are brutal in the summer for any strenuous actvity! Hope that helps.
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No, I am not Bear Grylls, but I stayed at a Holiday Inn Express last night and Bear was there too!