They also have/had a location near Oracle. Never saw anyone go in or out of there, just a Cemex sign at the highway and a gated entrance.
The address is 63514 E Hwy 77, Oracle AZ
Most of that is not underground. It an arroyo, or dry wash. It is a way to drain rain water out of the neighborhood so it doesn't flood the streets. Tucson has them all over in practically every neighborhood. The underground part is where it goes under a road. I'm not saying people didn't walk through the wash, but it isn't underground.