Historically distinct IANA time zone
America/Denver
- Countries
- United States of America
- GPS reference
- 39.74° N, 104.98° W
- Data source
- IANA northamerica
- Aliases
- America/Shiprock, MST7MDT, Navajo, US/Mountain
United States of AmericaMountain (most areas)
Geographic context
Where this clock belongs
The map marks the IANA reference location and associated country, not a time-zone boundary.
GPS reference: 39.74° N, 104.98° W. Associated countries: US.
The Wikipedia link provides additional context; it is not evidence for a historical claim. Transition data comes from the IANA source file.
Notes from the time database
The story behind the clock
These source notes describe a period or rule. They do not, by themselves, establish a causal claim for a particular clock change.
US mountain time, represented by Denver Colorado, far western Kansas, Montana, western Nebraska, Nevada border (Jackpot, Owyhee, and Mountain City), New Mexico, southwestern North Dakota, western South Dakota, far western Texas (El Paso County, Hudspeth County, and Pine Springs and Nickel Creek in Culberson County), Utah, Wyoming On 1921-03-04 federal law placed all of Texas into the central time zone. However, El Paso ignored the law for decades and continued to observe mountain time, on the grounds that that's what they had always done and they weren't about to let the federal government tell them what to do. Eventually the federal government gave in and changed the law on 1970-04-10 to match what El Paso was actually doing. Although that's slightly after our 1970 cutoff, there is no need to create a separate zone for El Paso since they were ignoring the law anyway. See: Long T. El Pasoans were time rebels, fought to stay in Mountain zone. El Paso Times. 2018-10-24 06:40 -06.
War
Peace
Original IANA source file: northamerica.
A shared present
Same clock today, different past
These nearby zones follow the same current annual pattern, yet retain their own historical record.
Mexico · 900 km from the reference location · Same annual clock since 2023
Canada · 3266 km from the reference location · Same annual clock since 2002Civil-time record
Recorded changes over time
From 1883 to 2027 · 138 recorded transitions
Recurring daylight-saving changes are grouped separately when JavaScript is available.
Notable changes
One-off changes and transitions outside the recurring seasonal rhythm.
- -07:00 · MSTStandard time applies
- -06:00 · MDTDaylight saving time begins
- -07:00 · MSTStandard time applies
- -06:00 · MDTDaylight saving time begins
- -07:00 · MSTStandard time applies
- -06:00 · MDTDaylight saving time begins
Browse every recorded transition
| Local time after transition | Offset after | Abbreviation | Rule |
|---|---|---|---|
| 1883-11-18 12:00 | -07:00 | MST | Standard time |
| 1918-03-31 03:00 | -06:00 | MDT | Daylight saving time |
| 1918-10-27 01:00 | -07:00 | MST | Standard time |
| 1919-03-30 03:00 | -06:00 | MDT | Daylight saving time |
| 1919-10-26 01:00 | -07:00 | MST | Standard time |
| 1920-03-28 03:00 | -06:00 | MDT | Daylight saving time |
| 1920-10-31 01:00 | -07:00 | MST | Standard time |
| 1921-03-27 03:00 | -06:00 | MDT | Daylight saving time |
| 1921-05-22 01:00 | -07:00 | MST | Standard time |
| 1942-02-09 03:00 | -06:00 | MWT | Daylight saving time |
| 1945-08-14 17:00 | -06:00 | MPT | Daylight saving time |
| 1945-09-30 01:00 | -07:00 | MST | Standard time |
| 1965-04-25 03:00 | -06:00 | MDT | Daylight saving time |
| 1965-10-31 01:00 | -07:00 | MST | Standard time |
| 1966-04-24 03:00 | -06:00 | MDT | Daylight saving time |
| 1966-10-30 01:00 | -07:00 | MST | Standard time |
| 1967-04-30 03:00 | -06:00 | MDT | Daylight saving time |
| 1967-10-29 01:00 | -07:00 | MST | Standard time |
| 1968-04-28 03:00 | -06:00 | MDT | Daylight saving time |
| 1968-10-27 01:00 | -07:00 | MST | Standard time |
| 1969-04-27 03:00 | -06:00 | MDT | Daylight saving time |
| 1969-10-26 01:00 | -07:00 | MST | Standard time |
| 1970-04-26 03:00 | -06:00 | MDT | Daylight saving time |
| 1970-10-25 01:00 | -07:00 | MST | Standard time |
| 1971-04-25 03:00 | -06:00 | MDT | Daylight saving time |
| 1971-10-31 01:00 | -07:00 | MST | Standard time |
| 1972-04-30 03:00 | -06:00 | MDT | Daylight saving time |
| 1972-10-29 01:00 | -07:00 | MST | Standard time |
| 1973-04-29 03:00 | -06:00 | MDT | Daylight saving time |
| 1973-10-28 01:00 | -07:00 | MST | Standard time |
| 1974-01-06 03:00 | -06:00 | MDT | Daylight saving time |
| 1974-10-27 01:00 | -07:00 | MST | Standard time |
| 1975-02-23 03:00 | -06:00 | MDT | Daylight saving time |
| 1975-10-26 01:00 | -07:00 | MST | Standard time |
| 1976-04-25 03:00 | -06:00 | MDT | Daylight saving time |
| 1976-10-31 01:00 | -07:00 | MST | Standard time |
| 1977-04-24 03:00 | -06:00 | MDT | Daylight saving time |
| 1977-10-30 01:00 | -07:00 | MST | Standard time |
| 1978-04-30 03:00 | -06:00 | MDT | Daylight saving time |
| 1978-10-29 01:00 | -07:00 | MST | Standard time |
| 1979-04-29 03:00 | -06:00 | MDT | Daylight saving time |
| 1979-10-28 01:00 | -07:00 | MST | Standard time |
| 1980-04-27 03:00 | -06:00 | MDT | Daylight saving time |
| 1980-10-26 01:00 | -07:00 | MST | Standard time |
| 1981-04-26 03:00 | -06:00 | MDT | Daylight saving time |
| 1981-10-25 01:00 | -07:00 | MST | Standard time |
| 1982-04-25 03:00 | -06:00 | MDT | Daylight saving time |
| 1982-10-31 01:00 | -07:00 | MST | Standard time |
| 1983-04-24 03:00 | -06:00 | MDT | Daylight saving time |
| 1983-10-30 01:00 | -07:00 | MST | Standard time |
| 1984-04-29 03:00 | -06:00 | MDT | Daylight saving time |
| 1984-10-28 01:00 | -07:00 | MST | Standard time |
| 1985-04-28 03:00 | -06:00 | MDT | Daylight saving time |
| 1985-10-27 01:00 | -07:00 | MST | Standard time |
| 1986-04-27 03:00 | -06:00 | MDT | Daylight saving time |
| 1986-10-26 01:00 | -07:00 | MST | Standard time |
| 1987-04-05 03:00 | -06:00 | MDT | Daylight saving time |
| 1987-10-25 01:00 | -07:00 | MST | Standard time |
| 1988-04-03 03:00 | -06:00 | MDT | Daylight saving time |
| 1988-10-30 01:00 | -07:00 | MST | Standard time |
| 1989-04-02 03:00 | -06:00 | MDT | Daylight saving time |
| 1989-10-29 01:00 | -07:00 | MST | Standard time |
| 1990-04-01 03:00 | -06:00 | MDT | Daylight saving time |
| 1990-10-28 01:00 | -07:00 | MST | Standard time |
| 1991-04-07 03:00 | -06:00 | MDT | Daylight saving time |
| 1991-10-27 01:00 | -07:00 | MST | Standard time |
| 1992-04-05 03:00 | -06:00 | MDT | Daylight saving time |
| 1992-10-25 01:00 | -07:00 | MST | Standard time |
| 1993-04-04 03:00 | -06:00 | MDT | Daylight saving time |
| 1993-10-31 01:00 | -07:00 | MST | Standard time |
| 1994-04-03 03:00 | -06:00 | MDT | Daylight saving time |
| 1994-10-30 01:00 | -07:00 | MST | Standard time |
| 1995-04-02 03:00 | -06:00 | MDT | Daylight saving time |
| 1995-10-29 01:00 | -07:00 | MST | Standard time |
| 1996-04-07 03:00 | -06:00 | MDT | Daylight saving time |
| 1996-10-27 01:00 | -07:00 | MST | Standard time |
| 1997-04-06 03:00 | -06:00 | MDT | Daylight saving time |
| 1997-10-26 01:00 | -07:00 | MST | Standard time |
| 1998-04-05 03:00 | -06:00 | MDT | Daylight saving time |
| 1998-10-25 01:00 | -07:00 | MST | Standard time |
| 1999-04-04 03:00 | -06:00 | MDT | Daylight saving time |
| 1999-10-31 01:00 | -07:00 | MST | Standard time |
| 2000-04-02 03:00 | -06:00 | MDT | Daylight saving time |
| 2000-10-29 01:00 | -07:00 | MST | Standard time |
| 2001-04-01 03:00 | -06:00 | MDT | Daylight saving time |
| 2001-10-28 01:00 | -07:00 | MST | Standard time |
| 2002-04-07 03:00 | -06:00 | MDT | Daylight saving time |
| 2002-10-27 01:00 | -07:00 | MST | Standard time |
| 2003-04-06 03:00 | -06:00 | MDT | Daylight saving time |
| 2003-10-26 01:00 | -07:00 | MST | Standard time |
| 2004-04-04 03:00 | -06:00 | MDT | Daylight saving time |
| 2004-10-31 01:00 | -07:00 | MST | Standard time |
| 2005-04-03 03:00 | -06:00 | MDT | Daylight saving time |
| 2005-10-30 01:00 | -07:00 | MST | Standard time |
| 2006-04-02 03:00 | -06:00 | MDT | Daylight saving time |
| 2006-10-29 01:00 | -07:00 | MST | Standard time |
| 2007-03-11 03:00 | -06:00 | MDT | Daylight saving time |
| 2007-11-04 01:00 | -07:00 | MST | Standard time |
| 2008-03-09 03:00 | -06:00 | MDT | Daylight saving time |
| 2008-11-02 01:00 | -07:00 | MST | Standard time |
| 2009-03-08 03:00 | -06:00 | MDT | Daylight saving time |
| 2009-11-01 01:00 | -07:00 | MST | Standard time |
| 2010-03-14 03:00 | -06:00 | MDT | Daylight saving time |
| 2010-11-07 01:00 | -07:00 | MST | Standard time |
| 2011-03-13 03:00 | -06:00 | MDT | Daylight saving time |
| 2011-11-06 01:00 | -07:00 | MST | Standard time |
| 2012-03-11 03:00 | -06:00 | MDT | Daylight saving time |
| 2012-11-04 01:00 | -07:00 | MST | Standard time |
| 2013-03-10 03:00 | -06:00 | MDT | Daylight saving time |
| 2013-11-03 01:00 | -07:00 | MST | Standard time |
| 2014-03-09 03:00 | -06:00 | MDT | Daylight saving time |
| 2014-11-02 01:00 | -07:00 | MST | Standard time |
| 2015-03-08 03:00 | -06:00 | MDT | Daylight saving time |
| 2015-11-01 01:00 | -07:00 | MST | Standard time |
| 2016-03-13 03:00 | -06:00 | MDT | Daylight saving time |
| 2016-11-06 01:00 | -07:00 | MST | Standard time |
| 2017-03-12 03:00 | -06:00 | MDT | Daylight saving time |
| 2017-11-05 01:00 | -07:00 | MST | Standard time |
| 2018-03-11 03:00 | -06:00 | MDT | Daylight saving time |
| 2018-11-04 01:00 | -07:00 | MST | Standard time |
| 2019-03-10 03:00 | -06:00 | MDT | Daylight saving time |
| 2019-11-03 01:00 | -07:00 | MST | Standard time |
| 2020-03-08 03:00 | -06:00 | MDT | Daylight saving time |
| 2020-11-01 01:00 | -07:00 | MST | Standard time |
| 2021-03-14 03:00 | -06:00 | MDT | Daylight saving time |
| 2021-11-07 01:00 | -07:00 | MST | Standard time |
| 2022-03-13 03:00 | -06:00 | MDT | Daylight saving time |
| 2022-11-06 01:00 | -07:00 | MST | Standard time |
| 2023-03-12 03:00 | -06:00 | MDT | Daylight saving time |
| 2023-11-05 01:00 | -07:00 | MST | Standard time |
| 2024-03-10 03:00 | -06:00 | MDT | Daylight saving time |
| 2024-11-03 01:00 | -07:00 | MST | Standard time |
| 2025-03-09 03:00 | -06:00 | MDT | Daylight saving time |
| 2025-11-02 01:00 | -07:00 | MST | Standard time |
| 2026-03-08 03:00 | -06:00 | MDT | Daylight saving time |
| 2026-11-01 01:00 | -07:00 | MST | Standard time |
| 2027-03-14 03:00 | -06:00 | MDT | Daylight saving time |
| 2027-11-07 01:00 | -07:00 | MST | Standard time |