- 2017 National Association of Geoscience Teachers. Conceptual models have long served as a means for physical geographers to organize their understanding of feedback mechanisms and complex systems. Analytical reasoning provides undergraduate students with an opportunity to develop conceptual models based upon their understanding of surface processes and environmental conditions. This study describes the use of analytical reasoning by junior and senior undergraduate students to predict the expansion and contraction of the South Texas Sandsheet as an example of this instructional technique. Students perceived that the analytical reasoning approach was significantly better for understanding desert expansion and contraction compared with the traditional lecture. A preliminary assessment of an analytical reasoning approach to desertification is presented as an example of how this approach can be incorporated into undergraduate geoscience courses.