Yes, but Santa Isabel is in the Mexicali municipality.  It’s a suburb.  Presumably they are on the same time zone.

So Santa Isabel isn’t in America/Santa_Isabel, and San Felipe is the largest locality that is.

From: Tim Parenti [mailto:tim@timtimeonline.com]
Sent: Wednesday, October 7, 2015 6:31 PM
To: Matt Johnson <mj1856@hotmail.com>
Cc: tz@iana.org
Subject: Re: [tz] America/Santa_Isabel

On 7 October 2015 at 21:03, Matt Johnson <mj1856@hotmail.com> wrote:

Wouldn't then America/San_Felipe be a better choice?

Presumably population as usual.  In 2010, San Felipe had a population of ~17,000, compared to Santa Isabel's ~29,000.

--
Tim Parenti