"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."
https://github.com/eggert/tz/commit/76d435a0dc801baf32d7e16d51fba417b60a10e4