Rhubarb Upside Down Cake

Butter a 13 x 9-inch pan. Cut 5 cups rhubarb into 1/2-inch pieces and lay in the pan. Sprinkle 1 1/2 cups sugar over the rhubarb. Then sprinkle with 1 (3 ounce) box raspberry gelatin and 3 cups miniature marshmallows. Mix 1 box white or yellow cake mix as per package directions and pour over the top. Bake at 350 degrees F for 1 hour.