The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time (UTC-8). The clock time in this zone is based on the mean solar time of the 120th degree meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.
In the United States and Canada, this time zone is generically called Pacific Time (PT). Specifically, it is Pacific Standard Time (PST) when observing standard time (Winter), and Pacific Daylight Time (PDT) when observing daylight saving time (Summer). In Mexico this time is known as the Northwest Zone.
The zone is one hour ahead of the Alaska Time Zone, one hour behind the Mountain Time Zone and three hours behind the Eastern Time Zone.
In the United States, the states of Washington and California are located entirely within the Pacific Time Zone. Nearly all of Nevada, except for the towns of West Wendover and Jackpot, is on Pacific Time. Additionally, the northern part of Idaho (the Idaho Panhandle) and all of Oregon except for the greater part of Malheur County are also in the zone. The exact specification for the location of time zones and the dividing line between zones is set forth in the Code of Federal Regulations at 49 CFR 71.
In Canada, PST includes almost all of the province of British Columbia (except for the Highway 95 corridor and portions around Fort St. John), all of the Yukon Territory and Tungsten, Northwest Territories.
In Mexico, the state of Baja California is wholly within and the only part of Mexico in PST. Also the westernmost of the Revillagigedo Islands (Colima), Clarion Island uses the Pacific Time Zone.
Most of the Pacific Time zone observes Pacific Daylight Time (PDT, UTC-7) during the summer months, with the exception of the areas surrounding Dawson Creek and Creston in British Columbia. Also, during summer months, most of Arizona, which is in the Mountain time zone but does not observe DST, have the same time as neighboring states to the west which are on Pacific daylight time.
Through 2006, the local time (PST, UTC-8) changed to PDT (UTC-7) at 02:00 LST (local standard time) to 03:00 LDT (local daylight time) on the first Sunday in April, and returned at 02:00 LDT to 01:00 LST on the last Sunday in October.
Effective 2007, the local time changes from PST to PDT at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November, except in Mexico, where the previous dates are still in effect.
