In 1831, when he was living in Taos, St. Vrain became a naturalized Mexican citizen; it enable him to avoid the restrictions placed on American traders in what was then Mexican territory. He soon afterward formed a partnership with American trader William Bent. The new company was known as Bent, St. Vrain & Company; the company's trading area covered much of Wyoming, New Mexico, Kansas, and Colorado. They established company trading posts in Santa Fe and Taos, where their wagon trains made deliveries of goods shipped from Independence and Westport, Missouri. They traded cloth, glass, hardware, and tobacco for silver, furs, horses, and mules.