UPDATE (7:23 p.m.) - California Highway Patrol reopened northbound lanes along Highway 101 on the Cuesta Grade.
According to Caltrans, they have completely cleared the highway of all the cardboard.
The cause of the incident is under investigation.
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UPDATE (5:53 p.m.) - According to the California Highway Patrol, the #2 lane of Highway 101 is partially open; however, it's expected to take a couple more hours to completely clear the highway of cardboard.
Traffic is beginning to back up into the city of San Luis Obispo.
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(3:55 p.m.) - An overturned trailer is causing a traffic backup over the Cuesta Grade.
The crash was reported just after 3:30 p.m. in the northbound lanes of Highway 101 near the Highway 58 offramp.
According to the California Highway Patrol, a semi-truck was towing a trailer that flipped, causing multiple boxes and pallets to fall into the roadway.
The #1 and #2 lanes of the highway are reportedly blocked, and it could take up to a couple of hours to clear the highway.
A SIG Alert has been issued warning of slow traffic through the area.
