The Mountain Time Zone of North America keeps time by subtracting seven hours from Greenwich
Mean Time, during the shortest days of autumn and winter, and by subtracting six hours during
daylight saving time in the spring, summer, and early autumn. The clock time in this zone
is based on the mean solar time at the 105th meridian west of the Greenwich Observatory.
In the United States, the exact specification for the location of time zones and the dividing
lines between zones is set forth in the Code of Federal Regulations at 49 CFR 71.
In the United States and Canada, this time zone is generically called Mountain Time.
Specifically, it is Mountain Standard Time when observing standard time, and Mountain
Daylight Time when observing daylight saving time. The term refers to the fact that the
Rocky Mountains, which range from northwestern Canada to the US state of New Mexico, are
located almost entirely in the time zone. In Mexico, this time zone is known as the
Pacific Zone. In the United States and Canada, the Mountain
Time Zone is one hour ahead of the Pacific Time Zone and one hour behind the Central
Time Zone. In some areas, starting in 2007, the local
time changes from MST to MDT at 2 am MST to 3 am MDT on the second Sunday in March
and returns at 2 am MDT to 1 am MST on the first Sunday in November.
Sonora in Mexico and most of Arizona in the United States do not observe daylight saving
time, and during the spring, summer, and autumn months they are on the same time as Pacific
Daylight Time. The Navajo Nation, most of which lies within Arizona, observes daylight
saving time, although the Hopi Nation, as well as some Arizona state offices lying within
the Navajo Nation, do not. The largest city in the Mountain Time Zone
is Ciudad Juárez, Chihuahua. The Phoenix metropolitan area is the largest metropolitan
area in the zone; the largest metropolitan area that observes Mountain Daylight Time
is the binational El Paso–Juárez area, closely followed by Denver, Colorado. TV broadcasting
in the Mountain Time Zone is typically tape-delayed one hour, so that shows match the broadcast
times of the Central Time Zone.
Canada
The following provinces and areas are part of the Mountain Time Zone:
Alberta the Northwest Territories
most of the Kitikmeot Region of Nunavut portions of southeastern and northeastern
British Columbia the area of Saskatchewan immediately surrounding
the city of Lloydminster
Mexico
The following states have the same time as Mountain Time Zone:
Baja California Sur Chihuahua
Nayarit: Except from the Bahía de Banderas municipality which uses the Central Time Zone.
Sonora – no daylight saving time, always on MST.
Sinaloa Revillagigedo Islands: three of the four islands
have the same time as Mountain Time Zone, Isla Socorro, San Benedicto Island and Roca
Partida.
United States
The following states or areas are part of the Mountain Time Zone:
Arizona – no daylight saving time, always on MST, except in the Navajo Nation.
Colorado Idaho – southern half, south of the Salmon
River Kansas – only the counties of Sherman, Wallace,
Greeley and Hamilton, all of which border Colorado. The remaining three counties that
border Colorado, Cheyenne, Morton and Stanton, observe Central Standard Time, as do all other
Kansas counties. Montana
Nebraska – western third Nevada – West Wendover, on the Utah border,
is the only location in the state which legally observes Mountain Time. However, the towns
of Jackpot, Jarbidge, Mountain City and Owyhee, while all legally within the Pacific Time
Zone, locally observe the Mountain Time Zone due to proximity to and stronger connections
with towns in nearby Idaho. New Mexico
North Dakota – southwestern quadrant, southwest of the
Oregon – most of Malheur County, on the Idaho border
South Dakota – western half Texas – the two westernmost counties
Utah Wyoming
Also, the unincorporated community of Kenton, Oklahoma, located in the extreme western end
of the Oklahoma Panhandle, unofficially observes Mountain Time. However, the entire state of
Oklahoma is officially in the Central Time Zone. Additionally, western Culberson County,
Texas unofficially observes Mountain Time. See also
Effects of time zones on North American broadcasting Notes
References
Sources World time zone map
U.S. time zone map History of U.S. time zones and UTC conversion
Canada time zone map Time zones for major world cities
The official U.S. time for the Mountain Time Zone
Official times across Canada Official times across Mexico