According to Adam Rodriguez, a subcontractor for freight-hauling railroad Union Pacific, the packages are stolen from trains by thieves.
"They jump on these trains, these locks that these containers have are really sometimes plastic seals, the locks aren't really strong", he told Reuters. "They don't care if the trains are moving or not, they jump on the trains, pop the locks and start grabbing whatever they see."
Some of the boxes are from Amazon and United Parcel Service. COVID-19 testing kits and other medical supplies are among the discarded packages.
A security guard from the nearby University of Southern California campus, who wished to remain anonoymous, told Reuters packages and debris were cleaned up thirty days ago, but have since returned.
He said he regularly patrols through the area to ensure students who wander down onto the railway tracks are not in danger.