TOPANGA, Calif. (KABC) -- Giant rocks came crashing down onto Topanga Canyon Boulevard in the Santa Monica Mountains, causing a closure that may last up to three days, Caltrans officials said Sunday evening.The roadway was closed in both directions at Old Topanga Canyon Road while crews tried to clear the giant boulders and shore up the hillside.Caltrans District 7 officials confirmed it could be two or three days before the road reopens again.The startling rock slides happened amid the strongest rainstorm Southern California experienced this week, following several weeks of wet weather in the area.