This dissertation seeks to answer two primary questions stemming from the war between the United States and Mexico: 1) What methods did the United States Army Quartermaster Department employ during the war to achieve their goals of supporting armies in the field? 2) In executing these methods, what lasting impact did the presence of the Quartermaster Department leave on the Lower Río Grande borderland, specifically South Texas during the interwar period from 1848-1860? In order to obtain a complete understanding of what the Department did during the war, a discussion of the creation, evolution, and methodology of the Quartermaster Department lays the foundation for effective analysis of the department's wartime methods and post-war influence. It is equally essential to understand the history of South Texas prior to the Mexican War under the successive control of Spain, Mexico and the United States and how that shaped the wartime situation. The wartime discussion of Department operations is divided into three chapters, reflecting each of the main theaters and illustrating the respective methods and influence within each area. The final two chapters address the impact of the war on South Texas and how the presence of the Quartermaster Department on the Río Grande served as a catalyst for economic, social, and political changes in this borderland region. Combining primary source analysis of wartime logistics with a synthesis of divergent military and social histories of the Lower Río Grande borderland demonstrates the influence of the Department on South Texas during the mid-nineteenth century. The presence of the Quartermaster Department created an economic environment that favored Anglo-American entrepreneurs, allowing them to grow in wealth and begin to supplant the traditional Tejano/Mexican-American power structure in South Texas. Despite remaining an ethnic minority, Anglos used this situational advantage to dominate the region politically. This outcome shaped South Texas for decades to follow.