PORTLAND -- It’s that time of year when rain comes to the Pacific Northwest and rock slides become a real public danger.

Oregon Department of Transportation crews are out along Highway 99 East, just south of Oregon City, shoring up a recent man-made slide.

Crews are actually prying massive boulders off a steep cliff and allowing them to tumble down into the highway.

Consequently, two lanes of traffic have been closed for safety concerns.

Crews are up on cranes using pry bars and special air bags to further loosen rocks they believe pose danger.

Transportation officials do this every year around this time. As the rain begins, the earth becomes saturated and boulders start to fall.

Just days ago boulders here along the highway fell on their own.

Geologists say that once one rock falls it can set off a string of slides. Transportation officials want to make sure the rocks are not falling into traffic.

"We have a great geo-tech team. Whenever rocks fall we send them out and they look at the entire area to see whether there are any other rocks that need to be removed so they don’t come tumbling down hurting anyone that might be driving by," said Christine Miles, a state transportation official.

ODOT says drivers can expect portions of traffic to be closed for safety reasons Friday and Saturday. Highway 99 also may be closed entirely at certain times during that time period.

Drivers can expect delays in both directions, officials say.

KGW Reporter Keely Chalmers contributed to this report.