San Juan forming the boundary between Colorado and New Mexico

The San Juan Mountains play a significant role in defining the boundary between Colorado and New Mexico. This mountain range, rich in natural beauty and resources, serves as a natural divider. The boundary generally follows the crest of the mountains, meaning that the land and geological features on one side belong to Colorado, while those on the other side belong to New Mexico. This geological demarcation has historical significance as it reflects territorial claims and divisions established during the United States' westward expansion, influencing regional identity and governance in both states.