The cellphone video, captured by an ABC30 insider, showed a makeshift living area.
Curtains appeared to be set up, along with pieces of wood on the floor and cans and bottles scattered throughout the confined space.
The video was taken days before a fire broke out Monday morning inside a bridge utility vault at Fresno and H streets in downtown.
Two people, believed to be from the unhoused community, were found dead inside.
Authorities identified the victims as 57-year-old Johnny Torres and 50-year-old Antonio Corona.
Investigators are still working to determine what caused the fire.
"It appears that they may have kind of tunneled in from the side of the embankment, that was the only visible access," said Josh Sellers with the Fresno Fire Department.
Sellers warned about the dangers of entering such spaces.
"The best advice is don't find yourself in that situation. Those are not designed for human occupancy, to go and live in there and seek shelter," he said.
Encampments along Central California freeways are not uncommon, but the video highlights how some may be hidden from view.
A similar situation last week in Southern California caused major disruptions when a trash fire near a homeless encampment broke out in a tunnel under the 110 Freeway, snarling traffic for hours.
In response to issues tied to encampments on state property, Gov. Gavin Newsom launched the State Action for Facilitation on Encampments, or "SAFE" Task Force, last year.
The initiative aims to remove encampments and connect unhoused individuals with housing and health services.
Since its launch, Caltrans has reported removing 22 encampments and clearing 948 cubic yards of debris.
The agency adds fencing, rocks and other deterrents have also been installed to prevent people from returning.
Action News reached out to Caltrans for further details on its cleanup and prevention efforts and is working on a response.
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