Archaeologists have been getting a look at the underground remains of ancient canals and irrigated fields in Phoenix as Sky Harbor International Airport has built its new Sky Train system and related facilities.

The analysis of the structures dating from around A.D. 400 to 500 is just the latest scientific explorations of systems long known to have been built and used by the Hohokam people to carry Salt River water to fields.

The Arizona Republic reports that Phoenix city archaeologist Laurene Montero says this is the first time that an actual field system was found and observed.

Artifacts discovered during the first phase of Sky Train construction are now undergoing analysis at a lab in Tucson. They'll be returned to the Pueblo Grande Museum in Phoenix.