New Mexico dumped Arizona 152 years ago today when the Arizona Territory was established. (Since 1850 New Mexico Territory had included both present-day states.)
In March 1861, following conventions in Mesilla and Tucson, the southern portion of New Mexico Territory declared its withdrawal from the Union. The Confederate congress approved and CSA President Davis proclaimed the action February 14, 1862. While all this had no legal force in the United States, it probably did influence the decision in Washington to create Arizona Territory. Congress passed a bill and President Lincoln signed it into law February 24, 1863.
The Confederate Arizona Territory consisted of the bottom half of both present-day states (dividing the two at 34ºN, just south of Socorro and Prescott). The U.S. Arizona Territory set 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 would have been the Grand Canyon State and Arizona would have had the Deming Duck Race.
The capital of the Confederate Arizona Territory was in Mesilla (near present-day Las Cruces). The first territorial capital of Arizona was Prescott.