The Forty-First Parallel North is a circle of latitude that is 41 degrees north of the Earth's equatorial plane. It runs across several countries, including the United States, where it passes through states like California, Nevada, Utah, Colorado, and New Jersey. This parallel is significant in geography as it helps to define climate zones and ecosystems. In addition to its geographical importance, the Forty-First Parallel North has historical relevance. It served as a boundary in various treaties and land claims, particularly during the westward expansion of the United States. The parallel is also notable for its proximity to major cities such as San Francisco and Philadelphia.