New Mexico dumped Arizona on this date in 1863 when the Arizona Territory was established.
In 1861, after March conventions in Mesilla and Tucson, the southern portion of New Mexico Territory followed the lead of the southern states and attempted to withdraw from the Union. The Confederate congress approved in 1862. While all this had no legal meaning in the United States, it probably did influence the decision to create the real Arizona Territory by February 24th the next year.
The Confederate Arizona Territory consisted of the bottom half of both present-day states (dividing the two at 34ºN). The U.S. Arizona Territory in 1863 made the division along the north-south border we have today (dividing at 109º 2′ 59.25″W). Too bad. With the Confederate division New Mexico could have been the Grand Canyon State and Arizona could have had the Deming Duck Race.
The capital of the Confederate Arizona Territory was in Mesilla (near present-day Las Cruces).