Heat oven to 350 degrees (F).
Generously butter and flour entire 9 x 13 inch baking pan.
In a large mixing bowl, combine sugar, baking soda, salt, and flour.
Stir in the beaten eggs and sour cream to the dry mixture.
Fold in the chopped rhubarb; the batter will be very thick and heavy.
Pour batter into prepared baking pan and spread it evenly throughout the pan.
In a small bowl, blend together the brown sugar and butter until well-blended.
Stir in ¼ cup flour and cinnamon, until mixture is sticky-crumbly.
Sprinkle streusel topping evenly over the unbaked cake batter.
Bake cake for 45 minutes or until an inserted toothpick comes out clean.