A rock slide temporarily closed a lane of traffic Thursday afternoon on Interstate 5 at the Siskiyou Summit, officials said.

A rock slide temporarily closed a lane of traffic Thursday afternoon on Interstate 5 at the Siskiyou Summit, officials said.

At around 4:30 p.m. three large rocks, one the size of a small car, and several smaller ones came crashing down the bluff near milepost 4 at a spot where truckers often stop to check their brakes before descending the summit, said Oregon Department of Traffic spokesman Gary Leaming.

"No cars were involved and no one was injured," Leaming said. "One of the rocks was big as a Volkswagon and the other two were half that size."

Leaming spoke Thursday evening with a geologist who determined the rocks at the top of the road cut had dried and cracked over the summer months, making them unstable.

The three largest boulders came to rest by the side of the freeway, while a number of smaller rocks rolled into the road. The southbound slow lane was closed for a little more than an hour as ODOT crews arrived to push them into the ditch, Leaming said.

ODOT workers used a large front loader to push the boulders further away from the road. ODOT crews might return to the area today to reduce the rocks with jackhammers or blow them up with a small charge, Leaming said.

About 15 cubic yards of rock slid from the bluff, Leaming said.

"In all it was enough to fill up a dump truck and a half," he said.

Landslides caused severe damage to the summit during a winter storm in December 2005. A five-mile stretch of the interstate from milepost 8 to milepost 13 saw damage to culverts and channels as boulders, rocks, trees and mud rushed onto the freeway. The cost of the damage was estimated at $2.4 million.

Reach reporter Chris Conrad at 776-4471; or e-mail cconrad@mailtribune.com.