It is now being investigated by researchers at the Sonoran Desert Museum, in Tucson, and was found in the Mid Cretaceous Turney Ranch Formation in Pima County, Arizona.

It was discovered in 1994 by Richard Thompson, a University of Arizona student, as he was hiking in a remote southern Arizona canyon looking for petrified wood.

This dinosaur belongs to a family of long necked sauropods called brachiosaurs. Since it is a new kind of brachiosaur paleontologists were able to assign this fossil a new taxonomic name, Sonorasaurus (from the Sonoran Desert) thompsoni (honoring Richard Thompson, the discoverer).

The age of the sandstone in which it was found appears to be Mid Cretaceous, about 100 million years old, and it appears that Sonorasaurus thompsoni may geologically be the youngest brachiosaur ever found. Named by Ratkevich in 1998.