At one time, Mexican food served east or west of State Street was destined to be watered down. The only really authentic Mexican food around town was often found in west-side eateries where local chefs catered to family, friends and a few gringos who knew just the right spot.

But with the widespread popularity of Mexican cooking during the past decade, aficianados of this colorful and lively cuisine can go just about anywhere around the valley and discover Mexican dishes that excite and occasionally inflame taste buds.Ads for Treasures of the Southwest in Sandy, not exactly an ethnic enclave, boast of "fresh homecooked Mexican food." The slick, stylish interior, including black lacquered chairs and mirrors on the wall, is hardly typical for a Southwest motif. (The prior tenant was Treasures of the Orient, an upscale Chinese restaurant that moved to another location.) Yet the decor itself could not distract diners from the sizzling scents wafting from the small open kitchen in the corner.

While the suburban minimall locale and chic motif may not set the stage for south of the border cooking, the menu is distinctly Mexican and Southwestern. Nachos, a traditional tlapeno soup, fajitas, chimichangas, tamales, burritos, enchiladas and tacos fill the menu. A few twists add to the Southwest slant, such as fried shrimp topped with jalapeno cheese sauce; Mexi-skins, potato skins stuffed with chorizo and cheddar cheese; and barbecued chicken wings with a smoked, honey flavor.

Prices are moderate, ranging from $1.95 for the tostada appetizer to $5 to $7 for most of the combination dinners. Southwest combination plates like the steak and shrimp, barbecued chicken and enchilada, or halibut and taquito cost up to $12.75.

Our experience was somewhat uneven in our sampling of four of the entrees and several of the appetizers. The piquant tomato salsa was fresh and flavorful; oddly it was lukewarm. (Had it sat on the table too long?) The guacamole was fresh and also nicely seasoned. Both of these selections possessed assertive spices.

We were unable to fully savor the black bean soup ($1.75), a pleasing bowl of tender black beans topped with salsa and sour cream mixed with bacon and chunks of chorizo. Our waitress brought it with our entrees. It was also barely warm.

There was no mistaking the heat of the seasoning with a few of the other entrees, especially the beef fajitas ($8.95) and the chile rellenos ($6.95). The latter was topped with a lively chile verde, rather than a milder homemade sauce as the menu had claimed. While the ample serving of beef chunks was tender with the fajitas, they were doused in a red chili sauce that obscured any of the other flavorings including the sauteed peppers and onions.

The same spiciness befell the shredded beef in the tacos on the New Mexico taco plate ($5.95). These were also not as appetizing as expected. The Navajo fry bread became soggy too quickly and most of the fillings, including the lettuce, shredded cheese, and guacamole, ended up on the plate.

The barbecued short ribs and tamale combination plate ($8.75) featured a somewhat ordinary 1/4 rack of ribs and tamale. The so-called Treasures rice, offered as a choice on some of the plates, was disappointingly tepid, devoid of any distinctive flavor and dotted (but hardly enhanced) by a few pieces of vegetables.

The ordinary quality of the homemade cheesecake ($2.95), sopapillas (50 each), and chocolate fudge cake ($2.95), concluded our meal.

Treasures of the Southwest features the kind of meal that would entice most diners who search for and relish Mexican food. It was, however, a treasure that was tarnished by inconsistent presentation and preparation.

Rating: * * 1/2

Treasures of the Southwest, 8623 S. 2000 East, (Fiesta Village). 942-8880. Open Monday through Friday, 11:30 a.m. until 2 p.m.; for dinner 5 to 9 p.m. Open until 10 p.m. on Friday and Saturday, closed Sunday. Accepts major credit cards and check with guarantee card.