Arizona

Arizona was a state of the United States of America. It was formerly a Spanish colony, and then briefly Mexican territory.

The First Doctor, Steven Taylor and Dodo Chaplet visited Arizona in October 1881. (TV: The Gunfighters)

In 1905, the Fifth Doctor, Tegan Jovanka and Turlough visited Buzzard Creek in Arizona. (AUDIO: Freakshow)

Circa 1969, the Second Doctor met with the crew of a Quotron spacecraft in the Arizona desert to keep their visit to Earth secret. (COMIC: U.F.O.)

In 1988, the Second Doctor, John and Gillian visited Arizona. (COMIC: The Faithful Rocket Pack)

Circa 2009, the Tenth Doctor and Donna Noble visited Arizona. (COMIC: Sting of the Serpent)

In 2012, the Seventh Doctor, Roz Forrester and Chris Cwej visited Arizona, where a gynoid transported Roz to New York in 1799. (PROSE: Christmas on a Rational Planet)

Behind the scenes
According to the pseudo-narrative Cybus Industries website, Arizona was still part of a United States of Mexico in Pete's World.