The legislation appears to make reference to a dividing line running parallel to and 20km south of the US border, plus Ensenada.
With Mexicali, it seems to refer to the town, not the larger municipality.
I also found two relatively recent articles from third parties:
Both have contact numbers - someone who speaks fluent Spanish (not me) could call and ask.
Note the first link has two tabs on the page, and the second tab has a map image. It's labeled with the 20km line - though they drew it poorly and placed it roughly around 250km in their image.
I don't think the zone should be deleted, just renamed. The backlink should probably point at the new name rather than at America/Tijuana, to reflect how we used it in the past. Otherwise, anyone using this zone in good faith will be adjusted with the wrong rules.
Keep in mind we did have it listed in zone.tab with comments as "Mexican Pacific Time - Baja California away from US border" - which would already have been shown via tzselect and others.
Date: Thu, 8 Oct 2015 08:51:29 -0400
From: arthurdavidolson@gmail.com
To: eggert@cs.ucla.edu
CC: tz@iana.org
Subject: Re: [tz] America/Santa_Isabel
We might expect that if the legislative intent was for the entirety of Baja California to use the U. S. rules, the legislation would have been written more simply.
That being said, it's certainly possible (or even probable) that de facto the entirety of Baja California uses U. S. rules, regardless of de jure.
Providentially, we're coming up on the days when a few international phone calls (or, if possible, monitoring radio or TV stations) can shed light on the matter.
But even if there are southern parts of Baja California that use Mexican rules, Santa_Isabel is almost surely the worng name.
@dashdashado