Shaded Relief Map of the Topographic Surface of Iowa This image map was created from the previous topographic data by shading the surface with an artificial light source shining from the northeast at an angle of 10 degrees above the horizon. This shading highlights topographic features trending in the northwest to southeast direction while minimizing features trending parallel to the light source. The rugged topography of northeast Iowa and the Loess Hills east of Missouri River floodplain in western Iowa show up well in this rendition. The large flat area in northcentral Iowa is called the Des Moines Lobe and marks the area of the last glacial advance into Iowa 12,000 to 14,000 years ago.