# Mountain Time Zone

The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time (UTC) when standard time (UTC−07:00) is in effect, and by subtracting six hours during daylight saving time (UTC−06:00). 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, Canada, and Mexico, 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 Rocky Mountains, which range from British Columbia to New Mexico. In Mexico, this time zone is known as the tiempo de la montaña or zona Pacífico ("Pacific Zone"). In the United States and Canada, the Mountain Time Zone is to the east of the Pacific Time Zone and to the west of 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.
Most of Mexico, and most of Arizona in the United States, do not observe daylight saving time (DST), and during the spring, summer, and autumn months they are on the same time as Pacific Daylight Time. The Navajo Nation is the only part of Arizona that observes DST. Its territory lies mostly within Arizona but extends into Utah and New Mexico (both observe DST statewide). Meanwhile, the Hopi Reservation, despite being completely surrounded by the Navajo Nation, does not observe DST, and neither do some Arizona state offices located within the Navajo Nation.
The largest city in the Mountain Time Zone is Phoenix, Arizona; the Phoenix metropolitan area is the largest metropolitan area in the zone. The largest city that observes daylight saving time is Juárez, Chihuahua, Mexico.

## Canada

One province and two territories are fully contained in the Mountain Time Zone:
* Alberta
* Northwest Territories
* Yukon (no DST)
On September 24, 2020, Yukon switched to the Mountain Standard Time year-round. Therefore, clocks in Yukon and Alberta are the same in the winter, and Alberta is one hour ahead in summer. Previously, the territory had used the Pacific Time Zone with daylight saving time: UTC−8 in winter and UTC−7 in summer.
One province and one territory are split between the Mountain Time Zone and the Pacific Time Zone:
* British Columbia – northeastern and southeastern regions
* Northwest Territories – Tungsten
One territory and one province are split between the Mountain Time Zone and the Central Time Zone:
* Nunavut: Kitikmeot Region
* Saskatchewan: Lloydminster and vicinity

## Mexico

As of October 30, 2022, Mexico abandoned daylight saving time, with certain exceptions.
The following states have an offset equal to Mountain Standard Time:
   * Baja California Sur
   * Nayarit: except for the Bahía de Banderas municipality, which uses the Central Time Zone.
   * Sonora
   * Sinaloa
   * Chihuahua: Observes Daylight Savings Time, only in northwestern border municipalities (Janos, Ascensión, Juárez, Guadalupe, and Práxedis Gilberto Guerrero)
   * Revillagigedo Islands (Colima): three of the four islands have the same time as Mountain Time Zone: Socorro Island, San Benedicto Island and Roca Partida.
The following states have an offset equal to Mountain Daylight Time:
| Aguascalientes Campeche Chihuahua Ciudad de México Coahuila Colima, except all of the Revillagigedo Islands. Chiapas Durango Guanajuato Guerrero | Hidalgo Jalisco México Michoacán Morelos Nuevo León Oaxaca Puebla Querétaro | San Luis Potosí Tabasco Tamaulipas Tlaxcala Veracruz Yucatán Zacatecas Municipality of Bahía de Banderas in Nayarit |

## United States

Six states are fully contained in the Mountain Time Zone:
* Colorado
* Montana
* New Mexico
* Utah
* Wyoming
* Arizona (does not use daylight saving time except for Navajo Nation)
Three states are split between the Mountain Time Zone and the Pacific Time Zone. The following locations observe Mountain Time:
* Idaho: Southern Idaho and the portion of Idaho County south of the Salmon River
* Oregon: the majority of Malheur County
* Nevada: West Wendover
Five states are split between the Mountain Time Zone and the Central Time Zone. The following locations observe Mountain Time:
* Kansas: Sherman, Wallace, Greeley and Hamilton counties
* Nebraska: western one third
* North Dakota: the southwest corner counties (Adams, Billings, Bowman, Golden Valley, Grant, Hettinger, Slope, Stark) observe MST. The counties of McKenzie, Dunn, and Sioux are split.
* South Dakota: western half
* Texas: El Paso, Hudspeth, and northwestern Culberson counties

## Major metropolitan areas

Alphabetical list of major cities located within the Mountain Time Zone. Cities in bold do not observe daylight saving time:
* Albuquerque, New Mexico
* Billings, Montana
* Boise, Idaho
* Boulder, Colorado
* Calgary, Alberta
* Cheyenne, Wyoming
* Ciudad Juárez, Chihuahua
* Ciudad Obregón, Sonora
* Colorado Springs, Colorado
* Culiacán, Sinaloa
* Metropolitan Denver
** Arvada, Colorado
** Aurora, Colorado
** Centennial, Colorado
** Denver, Colorado
** Lakewood, Colorado
** Westminster, Colorado
* Edmonton, Alberta
* El Paso, Texas
* Flagstaff, Arizona
* Fort Collins, Colorado
* Greeley, Colorado
* Hermosillo, Sonora
* La Paz, Baja California Sur
* Lake Havasu City, Arizona
* Las Cruces, New Mexico
* Lethbridge, Alberta
* Los Mochis, Sinaloa
* Mazatlán, Sinaloa
* Missoula, Montana
* Nogales, Sonora
* Metropolitan Phoenix
** Chandler, Arizona
** Gilbert, Arizona
** Glendale, Arizona
** Mesa, Arizona
** Peoria, Arizona
** Phoenix, Arizona
** Surprise, Arizona
** Tempe, Arizona
* Provo, Utah
* Pueblo, Colorado
* Rapid City, South Dakota
* Red Deer, Alberta
* Salt Lake City, Utah
* San Luis Río Colorado, Sonora
* Tepic, Nayarit
* Tucson, Arizona
* West Jordan, Utah
* West Valley City, Utah
* Yuma, Arizona