US States and Territories in the Mountain Time Zone

The Mountain Time Zone covers five full US states, parts of four others, most of Alberta, and a strip of northern Mexico. But the most common mistake people make is assuming Arizona follows the same clock as Denver. It doesn't.

Five States Fully in Mountain Time

Colorado, Montana, New Mexico, Utah, and Wyoming sit entirely inside the Mountain Time Zone. Every city, county, and town in these places uses Mountain Standard Time (MST) in winter and Mountain Daylight Time (MDT) in summer. Arizona is also fully inside the zone but never changes its clocks. That case is covered below.

State	IANA Zone	DST Observed?
Colorado	America/Denver	Yes
Montana	America/Denver	Yes
New Mexico	America/Denver	Yes
Utah	America/Denver	Yes
Wyoming	America/Denver	Yes

Major cities in these states include Denver (population 729,019), Albuquerque (564,559), Colorado Springs (456,568), and Aurora (359,407). For current local times, see the Time in Denver page.

States Split Between Mountain and Other Time Zones

Four US states are split. Part of the state runs on Mountain Time; the other part runs on Pacific or Central Time.

Idaho: North on Pacific, South on Mountain

The northern Idaho panhandle, including Coeur d'Alene and Moscow, observes Pacific Time (America/Los_Angeles). The rest of the state, including Boise, uses Mountain Time (America/Boise). The boundary follows the Salmon River roughly. Time in Boise shows Mountain Time.

Kansas: Four Counties on Mountain Time

Western Kansas is split by the Mountain-Central boundary. Four counties run on Mountain Time: Sherman, Wallace, Greeley, and Hamilton. The rest of Kansas is Central Time. These four counties sit along the Colorado border. Drive east out of Colorado into Kansas and you stay on Mountain Time for about 40 miles before hitting Central.

Oregon: One County on Mountain Time

Malheur County in eastern Oregon observes Mountain Time. The rest of Oregon is Pacific Time. Malheur County borders Idaho and Nevada. Its largest town is Ontario. The county chose Mountain Time to align with its trading partners in Idaho.

Nevada: One City on Mountain Time

West Wendover, Nevada, sits right on the Utah border. The town uses Mountain Time (America/Denver) to match Wendover, Utah, just across the state line. The rest of Nevada is Pacific Time.

Texas: El Paso and Hudspeth County

El Paso (population 678,815) and Hudspeth County are in the Mountain Time Zone. Everything east of Hudspeth County is Central Time. El Paso is the largest US city on Mountain Time that is not in a fully Mountain state. Its zone is America/Denver.

Arizona's Special Status Within the Zone

Arizona is the only US state in the Mountain Time Zone that does not observe daylight saving time. Arizona stays on MST (UTC−7) year-round. This creates a practical problem: from March to November, Arizona has the same clock reading as Los Angeles (Pacific Daylight Time) but is not on Pacific Time. It is still on Mountain Standard Time.

The rule has one exception: the Navajo Nation, which covers northeastern Arizona, does observe daylight saving time. The Hopi Reservation, surrounded by the Navajo Nation, does not. This creates a DST "doughnut" inside Arizona. For a full explanation, see Why Doesn't Arizona Observe Daylight Saving Time?.

Major cities on MST year-round: Phoenix (population 1,650,070), Tucson (542,629), Mesa (471,825), Chandler (260,828), Gilbert (247,542), Glendale (240,126), Scottsdale (236,839). See Time in Phoenix for the current clock.

Mountain Time Counties in Otherwise Central or Pacific States

The table below summarizes every county and city that breaks from its state's dominant time zone.

State	Entity on Mountain Time	Rest of State
Kansas	Sherman, Wallace, Greeley, Hamilton counties	Central Time
Oregon	Malheur County	Pacific Time
Nevada	West Wendover	Pacific Time
Texas	El Paso, Hudspeth County	Central Time
Idaho	Southern Idaho (including Boise)	Northern Idaho (Pacific)

Canadian Provinces and Mexican States on Mountain Time

Canada

The province of Alberta is fully on Mountain Time. Major cities: Calgary (population 1,306,784) and Edmonton (1,010,899). The IANA zone is America/Edmonton. See Time in Calgary.

Parts of British Columbia also use Mountain Time. The Peace River Regional District, including Fort St. John and Dawson Creek, runs on MST year-round with no DST. The town of Lloydminster, split between Alberta and Saskatchewan, follows Alberta's Mountain Time.

Mexico

The northern border strip of Chihuahua uses Mountain Time. The major city is Ciudad Juárez (population 1,512,450), directly across the border from El Paso, Texas. Ciudad Juárez observes DST to stay aligned with El Paso, even though Mexico abolished DST nationally in 2023. The IANA zone is America/Ciudad_Juarez. See Time in Ciudad Juárez.

Map of the Mountain Time Zone Boundary

The Mountain Time Zone roughly follows the 105th meridian west of Greenwich. The boundary zigzags to keep communities and economic regions together.

The east boundary separates Mountain from Central Time. It runs through western Kansas, the Oklahoma Panhandle, and west Texas. The west boundary separates Mountain from Pacific Time. It runs through central Idaho, eastern Oregon, and western Nevada. The north covers Alberta and northeast British Columbia. The south covers the northern border of Chihuahua, Mexico.

The next clock change for most of the zone is Sunday, March 14, 2027, at 02:00 local time, when clocks spring forward 60 minutes from MST (UTC−7) to MDT (UTC−6). Arizona and the parts of British Columbia that skip DST will not change. If you are scheduling anything across the Mountain Time Zone after that date, check whether the other party is in Arizona first.