Answer:
President Buchanan did not have any specific words on stopping Americans from crossing the Rockies. In fact, he supported the concept of Manifest Destiny and the expansion of American territory, which included the western regions beyond the Rockies.
Step-by-step explanation:
Manifest Destiny was a belief in the mid-19th century that the United States was destined to expand its territory from coast to coast. President James K. Polk was a strong proponent of Manifest Destiny, and during his presidency (1845-1849), the United States acquired Texas, Oregon, California, and other western territories. President Buchanan succeeded Polk in 1857, and he also supported the concept of Manifest Destiny. Therefore, it is unlikely that he would have expressed any opposition to Americans crossing the Rockies, as this was a key part of the westward expansion of the United States.