I've been cooking fajitas for as long as I can remember, at least since I could reach the grill and use a pair of tongs. But what spices are considered appropriate for this dish? While researching this dish I discovered that the name "fajitas" really refers to the part of the cow the cut comes from (I don't mean to offend, just inform). The spices for this dish really are regional.
In my region of the Southwest we use a base of chili powder, garlic, oregano, and coriander. In every kitchen I cooked in, the mix was essentially the same. I can't even say this spice mix is regional. Like garam masala or curry spices, the mix may have started out regional, but over the years has become a universal blend of spices.