The meridian 120° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The 120th meridian west forms a great circle with the 60th meridian east.
In Canada the border between British Columbia and Alberta is defined by the meridian north of where it intersects the Continental Divide of the Americas, and in the United States part of the border between California and Nevada follows it.
The mean solar time at this meridian determines the time for the Pacific Time Zone during standard time. Most of the year however, it is the meridian for Alaska Daylight Time, as daylight saving time is observed for two-thirds of the year.
Starting at the North Pole and heading south to the South Pole, the 120th meridian west passes through:
| Co-ordinates | Country, territory or sea | Notes |
|---|---|---|
| Arctic Ocean | ||
| Northwest Territories — Prince Patrick Island | ||
| M'Clure Strait | ||
| Northwest Territories — Banks Island | ||
| Prince of Wales Strait | ||
| Amundsen Gulf | ||
| Nunavut Northwest Territories — passing through Great Bear Lake British Columbia / Alberta border — from British Columbia — from Intersection Mountain at ; at this point the meridian meets the Continental Divide, and the boundary with Alberta diverts southeast | ||
| Washington Oregon — from California / Nevada border — from California — from, through South Lake Tahoe and just east of Madera | ||
| Pacific Ocean | Santa Barbara Channel | |
| California — Santa Rosa Island | ||
| Pacific Ocean | ||
| Southern Ocean | ||
| Antarctica | Unclaimed territory | |
See main article: 1872 California-Nevada State Boundary Marker. When California attained statehood in 1850, it adopted 120th meridian west as its eastern border.[1] [2] Between 1855 and 1900 there were six surveys to locate 120 degrees, with each locating the line of longitude differently.[3] In 1872, Alexey W. Von Schmidt undertook the survey of the state line. He marked his survey line with stones, wood, and iron markers; the only one who placed such markers[3] A new survey in 1893 showed that the Von Schmidt line was 1,600 to 1,800 feet west of the actual 120 degrees. However, California and Nevada both recognize the 1872 Von Schmidt survey and the 1893 survey as the state line.[3] Google maps shows that the Verdi, Nevada California–Nevada boundary marker, located at 39.5245°N -120.0019°W, is approximately west of 120 degrees longitude, with a similar deviation along the length of the line from Oregon to Lake Tahoe.
On the same day that it admitted California, Congress established a territorial government in the area immediately to the east. The organic Act for that new Territory -- which was then called Utah -- stated that it was to be "bounded on the west by the State of California." Act of Sept. 9, 1850, 9 Stat. 453. Eleven years later, the Territory of Nevada was created out of Utah. Congress indicated in the organic Act that Nevada might include portions of what was then California, but with the proviso that
"so much of the Territory within the present limits of the State of California shall not be included within this Territory until the State of California shall assent to the same by an act irrevocable without the consent of the United States. . . ."
Act of Mar. 2, 1861, 12 Stat. 210. No assent was ever given by California. Accordingly, when Nevada was admitted as a State in 1864, its western boundary and California's eastern one remained congruent.
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