Arizona picked up a third district after the 1960 Census. It encompassed the entire northern portion of the state, essentially wrapping around Phoenix and Maricopa County (the 1st district). After a mid-decade redistricting in 1967, the 3rd absorbed a slice of western Maricopa County, including most of what became the West Valley.
https://en.wikipedia.org/wiki/Arizona%27s_3rd_congressional_district
