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 much of the border between British Columbia and Alberta is defined by the meridian, and in the United States part of the border between California and Nevada approximately follows it.
The mean solar time at this meridian determines the time for the Pacific Time Zone (UTC−08:00) during standard time. Most of the year however, it is the meridian for Alaska Daylight Time, as daylight saving time is observed for nearly 2/3 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 | ||
| Canada | Northwest Territories - Prince Patrick Island | |
| M'Clure Strait | ||
| Canada | Northwest Territories - Banks Island | |
| Prince of Wales Strait | ||
| Amundsen Gulf | ||
| Canada | Nunavut Northwest Territories - passing through Great Bear Lake British Columbia / Alberta border - south of the 60th parallel north British Columbia - at Intersection Mountain () the meridian meets the Continental Divide, and the boundary with Alberta diverts southeast |
|
| United States | Washington Oregon California / Nevada border (approximate) California |
|
| Pacific Ocean | Santa Barbara Channel | |
| United States | California - Santa Rosa Island | |
| Pacific Ocean | ||
| Southern Ocean | ||
| Antarctica | Unclaimed territory |
|
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