Mountain Time Zone
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time (UTC) when standard time is in effect, and by subtracting six hours during daylight saving time (UTC−6). 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.[a]
|Mountain Time Zone|
MST or UTC−07
|Observance of DST|
|DST is observed in certain regions of this time zone between the 2nd Sunday in March and the 1st Sunday in November.|
|DST began||Mar 12, 2017|
|DST ends||Nov 5, 2017|
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, and Mountain Daylight Time (MDT) 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 Zona Pacifico.
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, does observe DST, 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. The Phoenix metropolitan area is the largest metropolitan area in the zone; the next 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 (i.e. prime time begins at 7 pm MT following the same order of programming as the Central Time Zone).
Only one Canadian province is fully contained in the Mountain Time Zone:
One province and one territory is split between the Mountain Time Zone and the Pacific Time Zone:
One territory and one province is split between the Mountain Time Zone and the Central Time Zone
The following states have the same time as Mountain Time Zone:
- Baja California Sur
- Nayarit: Except for the Bahía de Banderas municipality, which uses the Central Time Zone.
- Sonora – no daylight saving time, always on MST.
- Revillagigedo Islands (Colima): three of the four islands have the same time as Mountain Time Zone, Isla Socorro, San Benedicto Island and Roca Partida.
Five states are fully contained in the Mountain Time Zone:
Three states are split between the Mountain Time Zone and the Pacific Time Zone:
- Idaho – Southern Idaho
- Nevada – only West Wendover along with Idaho border towns Jackpot, Mountain City, Owyhee, and Jarbidge.
- Oregon – primary time zone for Malheur County
Seven states are split between the Mountain Time Zone and the Central Time Zone:
- "49 CFR 71.8 Mountain zone". Code of Federal Regulations. Retrieved October 7, 2011.
- "49 CFR 71.7 Boundary line between central and mountain zones". Code of Federal Regulations. Retrieved October 7, 2011.
- "49 CFR 71.9 Boundary line between mountain and Pacific zones". Code of Federal Regulations. Retrieved October 7, 2011.
- Robbins, Ted (March 11, 2007). "Arizona Says No to Daylight-Saving Time". National Public Radio. Retrieved June 18, 2012.