Traffic on a stretch of a key east-west highway in Colorado won't be back to normal for weeks after boulders the size of small cars crashed onto the roadway, according to officials who added Wednesday that workers were still finding large amounts of loose rock days after the initial slide.

Monday's slide on Interstate 70 about 125 miles east of the Utah border damaged a tractor-trailer but caused no injuries. The highway has since been shut in both directions from Glenwood Springs in the west to Gypsum in the east, forcing travelers to take detours of up to four hours. The four-lane stretch carries a daily average of 300 vehicles per hour through the canyon, Colorado Department of Transportation spokeswoman Amy Ford said.

Earlier Wednesday, the Colorado Department of Transportation, known as CDOT, had said one lane was expected to open Thursday. On Wednesday afternoon, officials said workers were finding so much loose rock that it was unclear the road would be safe for traffic on Thursday. In addition, rain and wind are predicted in the area Thursday.

Ford said travelers should check the transportation department website for proper routes after reports that some drivers used maps and GPS devices to find their own way around the slide and ended up in mountain passes usually closed during the winter.

Hundreds of cars and several tractor-trailers lined up Tuesday at a gate closing one of those passes, the Post Independent newspaper in Glenwood Springs reported (http://tinyurl.com/gwl5jyn ).

Pitkin County sheriff's Deputy Marcin Debski directed traffic at Independence Pass in Aspen and said he had "never seen anything like it."

Tumbling rocks have closed the stretch of I-70 several times in the past. A 2010 rock slide tore gaping holes in an elevated section of the road, closing the canyon for nearly four days and causing food shortages because delivery trucks were not able to reach restaurants and grocery stores.

In 2004, more than three dozen boulders landed on the highway. A slide in 1995 killed three people, and a boulder crashed onto a pickup truck in 1985, critically injuring a 5-year-old boy.

CDOT said the Glenwood canyon is among 750 areas prone to slides that it closely monitors. Slides are particularly common when cold periods are followed by warm spells and ice begins to melt.

The state spends some $8.5 million dollars a year on work to prevent and respond to rock falls across Colorado, CDOT officials said Wednesday, adding they could not immediately say how much of that was spent on Glenwood canyon.