TUCSON, Arizona — Frustration among volunteers searching for Nancy Guthrie has led them to take matters into their own hands. They have been scouring the desert ditches littered with trash and exploring homeless camps near her residence in hopes of uncovering any hints about her whereabouts.

On Sunday, the volunteers might have found a significant lead. A black backpack was discovered just two miles from Guthrie’s home.

Present at the scene on Sunday morning, The Post witnessed the discovery of the torn black Swiss Gear backpack in a storm drain that also serves as a makeshift shelter for the homeless.

This location is a brief drive away from the home of 84-year-old Nancy, situated in the Catalina Foothills neighborhood, north of Tucson.

Volunteer Catherine Lopez stumbled upon the backpack around 11 a.m. in a tunnel off West Orange Grove Road, near State Route 77.

She promptly contacted the Pima County Sheriff’s Office, and a deputy was on the scene within approximately 15 minutes.

A picture from the scene shows Lopez holding the backpack on a large stick while on the phone with the sheriff’s office.

Another photograph shows an officer wearing gloves gingerly picking up the closed backpack.

Two homeless people were in the storm drain at the time of the discovery, but the arrival of the authorities reportedly spooked them, and they fled the scene.

It doesn’t appear to be the same backpack as the masked perp wore in surveillance footage from Nancy’s Nest camera earlier this month.

This week, investigators identified the backpack as a black Ozark Trail Hiker, sold exclusively at Walmart.

Yet another glove was also found nearby on Sunday, just off North First Avenue.

It comes as Pima County Sheriff Chris Nanos faces accusations that his ego is derailing the hunt for Nancy, whose daughter, “Today” show host Savannah Guthrie, 54, flew out to Arizona at the start of the month to aid the search.

With no suspects or persons of interest identified, more than three weeks after Nancy was reported missing on Feb. 1, authorities are set to scale back the search in the coming days.