Preheat oven to 350ºF. Grease and lightly flour a 9” square baking pan.
In a medium bowl, combine flour, graham cracker crumbs, sugar, butter, and salt. Beat at low speed, scraping bowl often, until mixture is crumbly, 1-2 minutes. Stir in nuts, Press ½ of crumb mixture on bottom of prepared pan. Bake 10-12 minutes or until golden. Remove from oven.
Spread caramel topping over hot crust. Sprinkle walnuts, mini-marshmallows, and chocolate chips over caramel topping. Sprinkle remaining crumble mixture over top. Bake 10-12 minutes or until marshmallows just start to brown. Cool on rack about 30 minutes. Cover: refrigerate for 2 hours or until firm. Cut into bars.