In a large bowl, mix together the ranch dressing, salsa, yogurt, and taco seasoning. Mix well. Spread on the bottom of a large, shallow dish or pie plate. Top with shredded lettuce, tomatoes, and shredded cheese. Sprinkle the crumbled tortilla chips all over top. Refrigerate until ready to serve. Note: You can make the dip in advance, without the toppings and refrigerate for several days. Add toppings, before serving.