Mtn/Cntrl border at Fort Pierre South Dakota (also Pac/Mtn border at Winterhaven California)

Zoidiasoft Tech tech at
Thu Apr 7 11:13:10 UTC 2011

Vidal, California also observes America/Phoenix rules.  I experienced this personally while camped there in late 2009 - early 2010, but Vidal Junction is on America/Los Angeles.  My cell phone was indicating this and it also seems that the few people in that ghost town of Vidal work in Parker, AZ.

Curtis Manwaring
  ----- Original Message ----- 
  From: Steve Jones 
  To: tz at ; tz at ; tz at 
  Sent: Thursday, April 07, 2011 12:45 AM
  Subject: Mtn/Cntrl border at Fort Pierre South Dakota (also Pac/Mtn border at Winterhaven California)

  At 10:03 3/23/2011, Steve Jones wrote:

    The current Mountain/Central boundary in the most recent official US DOT description (49CFR71.7,, has the border running right through Fort Pierre South Dakota.

  A follow up:

  In the above I made a major error by failing to recognize the significance of this part of 49CFR71.7:

    (g) Points on boundary line. All municipalities located upon the zone boundary line described in this section are in the mountain standard time zone, except Murdo, S. Dak., which is in the central standard time zone.

  So all of the municipality of Fort Pierre is indeed within the Mountain Time zone.

  Today I released v1.05, which includes my interpretation of the Fort Pierre anomaly, as well as a similar situation in Winterhaven California, which, in respect to proximity to Yuma AZ, observes what it calls "Arizona Time" (Mountain Standard Time) year round.

  Here is what the site says about these changes:

    SD: The city of Fort Pierre (legally in the Mountain time zone) and a large radius on the west side of the Mountain/Central border observes Central time. Research determined that the distance this observance extends to the west is a matter of disagreement among the locals. After some effort to get a definitive answer I gave up and arbitrarily selected 20 miles, though I heard credible opinions that it stretched out as much as 50 miles. There are no services and very few residents in the western part of Stanley county, so the point is somewhat moot.

    CA: Winterhaven California, in deference to its proximity to Yuma AZ, observes Mountain Standard Time year round. This means that (like AZ) Winterhaven does not observe Daylight Saving time. So this puts Winterhaven ahead of California by one hour (in sync with Arizona) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is locally considered to be the "All American Canal". 

  I hope this information is of use to some here.


  Steve Jones 
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