Look for these:
The Feast of Santa Fe, Cooking of the American Southwest, Huntley Dent, Simon & Schuster, 1985
Cuisine of the American Southwest, Anne Lindsay Greer, Harper & Row, 1983 (won Tastemaker Award for Best Cookbook that year).
The Western Junior League Cookbook, Ann Seranne, Editor, David McKay Company, Inc., 1979. This includes all of the west, including the southwest.
Any southwest cookbook is going to be very heavily influenced by Mexican cuisine, although hopefully not Tex-Mex.