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The 120th meridian west, a line of longitude designated as 120° west of the Prime Meridian (also known as the Greenwich Meridian), traces a path from the absolute zenith of the North Pole down to the nadir of the South Pole. This imaginary line bisects the Arctic Ocean, traverses the vast expanse of North America, crosses the immense Pacific Ocean, navigates the challenging Southern Ocean, and finally concludes its journey across the frozen continent of Antarctica. It is a fundamental component of the global geographic coordinate system, essential for pinpointing locations on Earth.
Geometrically, the 120th meridian west forms a great circle with its diametrically opposite counterpart, the 60th meridian east. This relationship is crucial for understanding global navigation and timekeeping.
Defining Borders and Territories
The significance of the 120th meridian west extends beyond mere cartography; it serves as a definitive boundary marker for several political entities. In Canada, this meridian meticulously delineates a portion of the border between the provinces of British Columbia and Alberta. This demarcation follows the meridian northward from where it intersects the Continental Divide of the Americas. Further south, in the United States, the 120th meridian west forms a significant segment of the border between the states of California and Nevada.
Beyond terrestrial boundaries, this meridian plays a role in the regulation of air traffic. It serves as the eastern boundary for the Oakland Oceanic and Tahiti flight information regions, and concurrently, acts as the western limit for the Mazatlan Oceanic FIR. This division ensures orderly and safe air travel across vast oceanic expanses.
Temporal Significance: The Pacific Time Zone
The 120th meridian west holds particular importance in the context of timekeeping, specifically for the Pacific Time Zone in North America. The mean solar time observed at this meridian historically dictates the standard time for this zone, which is designated as UTC−08:00 during standard time. However, the observance of daylight saving time means that for approximately two-thirds of the year, the meridian effectively governs Alaska Daylight Time, a variation that shifts the time zone forward. This temporal connection underscores the meridian's practical impact on daily life for millions.
From Pole to Pole: A Geographical Traverse
The journey of the 120th meridian west from the North Pole to the South Pole is a geographical odyssey, passing through a diverse array of landscapes and waters.
Starting at the apex of the world, the meridian descends through the frigid expanse of the Arctic Ocean. Its path then intersects with Canada, specifically touching upon Prince Patrick Island in the Northwest Territories. The meridian continues its southward course, bisecting the M'Clure Strait and later Banks Island, also within the Northwest Territories. It then cuts through the Prince of Wales Strait and the expansive Amundsen Gulf, before re-emerging onto Canadian land.
Upon reaching mainland Canada, the 120th meridian west traverses Nunavut and the Northwest Territories, notably passing through the vast Great Bear Lake. Its most significant terrestrial role in Canada emerges as it forms the border between British Columbia and Alberta. This border segment commences north of the Continental Divide, near Intersection Mountain, where the meridian meets the divide. At this juncture, the boundary between British Columbia and Alberta deviates southeastward, no longer following the strict north-south line of the meridian.
Continuing into the United States, the 120th meridian west first grazes the state of Washington before forming a substantial part of the border between Oregon and California, and subsequently between Nevada and California. Its passage through California is notable, cutting through the eastern Sierra Nevada and influencing the geography around South Lake Tahoe. It passes just to the east of Madera, California, before eventually meeting the vastness of the Pacific Ocean.
The meridian's oceanic passage includes the Santa Barbara Channel, where it intersects Santa Rosa Island, California, before continuing its southward journey across the Pacific.
The meridian's final terrestrial encounter is with Antarctica, where it traverses unclaimed territory before reaching the South Pole.
Discrepancies at the California–Nevada Border
The precise establishment of the California–Nevada border along the 120th meridian west has been a surprisingly contentious and historically complex issue, marked by surveying challenges and persistent discrepancies. Upon California's admission to the Union in 1850, the state constitution designated the 120th meridian west as its eastern boundary. However, the practical implementation of this definition proved far more intricate.
Between the years 1855 and 1900, a staggering six distinct surveys were undertaken in an attempt to accurately locate the 120-degree line of longitude. Each of these surveys, due to the limitations of contemporary surveying technology and the rugged terrain, yielded slightly different results, placing the meridian at varying positions.
A pivotal survey was conducted in 1872 by Alexey W. Von Schmidt. He meticulously marked his surveyed line with physical markers—stones, wood, and iron—a level of detail unmatched by other surveyors. Despite his efforts, a subsequent survey in 1893 revealed that the Von Schmidt line was, in fact, between 1,600 and 1,800 feet west of the true 120th meridian. Nevertheless, a peculiar compromise was reached: both California and Nevada agreed to recognize both the 1872 Von Schmidt survey and the 1893 survey as the definitive state line, effectively creating a boundary that did not perfectly align with the intended meridian.
Modern mapping, such as that provided by Google Maps, illustrates these enduring discrepancies. The Verdi, Nevada California–Nevada boundary marker, for instance, is situated approximately 525 feet (160 meters) west of the 120th meridian. Similar deviations are observed along the entire length of the border from Oregon down to the shores of Lake Tahoe, a testament to the historical challenges in precisely defining this significant geographical line. This ongoing, albeit largely administrative, divergence highlights how even seemingly straightforward geographical definitions can become entangled with historical precedent and political compromise.