Mountain Time Zone

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 (UTC−07), and by subtracting six hours during daylight saving time in the spring, summer, and early autumn (UTC−06). 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 and Canada, this time zone is generically called Mountain Time (MT). Specifically, it is Mountain Standard Time (MST) when observing standard time (winter), and Mountain Daylight Time (MDT) when observing daylight saving time (spring, summer, fall). 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 U.S., 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.

The 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 2:00am MST to 3:00am MDT on the second Sunday in March and returns at 2:00am MDT to 1:00am MST on the first Sunday in November.

Most of Arizona does not observe daylight saving time, and during the spring, summer, and autumn months it is on the same time as Pacific Daylight Time. The Navajo Nation, most of which lies within Arizona, does observe 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 Phoenix, Arizona, and its metropolitan area is the largest in the zone. The largest city that observes Mountain Daylight Time is 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 (i.e. prime time begins at 7:00 pm MT following the same order of programming as the Central time zone).

Canada
The following provinces and areas are part of the Mountain Time Zone:


 * Alberta
 * the Northwest Territories (except for Tungsten)
 * 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 (Colima): 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 (winter time), 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 – the border towns of West Wendover (near Utah) and Jackpot (near Idaho)
 * New Mexico
 * North Dakota – southwestern quadrant, southwest of the (Missouri River)
 * Oregon – most of Malheur County, on the Idaho border
 * South Dakota – western half
 * Texas – the two westernmost counties (Hudspeth, El Paso)
 * Utah
 * Wyoming

Also, the unincorporated community of Kenton, Oklahoma, located in the extreme western end of the Oklahoma Panhandle, unofficially observes Mountain Time (as the nearest sizeable towns are located in Colorado and New Mexico, both of which are in the Mountain Time Zone). However, the entire state of Oklahoma is officially in the Central Time Zone. Additionally, western Culberson County, Texas unofficially observes Mountain Time.