The Altar Valley is a 45-mile (72 km) long north-south valley, trending slightly northeast from Sasabe, Arizona on the Mexico border to the Avra Valley west of the Tucson Mountains. It is delimited by Arizona State Route 86, from east-to-west on the north separating it from the Avra Valley which then trends "northwesterly", merging into the plains and drainage of the Santa Cruz River.
The Altar Valley is 72 miles long.
The text says the Altar Valley is a 45-mile (72 km) long valley, so it looks like the algorithm mixed up miles and kilometers.