No one was injured by the wayward rock, described to be the size of a Volkswagen.
Highway 285 was closed in both directions at Parmalee Gulch Road west of C-470 until 10:45 p.m. on Tuesday.
"It just sounded like a freight train coming, next thing I know the big boulder landed in front of me," said Steven Jones, a trucker. "I was thanking the good Lord I wasn't anywhere further up the street than I was."
"I wouldn't want to be under it," Colorado State Patrol trooper Gilbert Mares said of the stone.
Mares said motorists were forced to use the northbound lane to go around the boulder until the highway was closed.
The Colorado Department of Transportation used explosives to blow the boulder apart on Tuesday night so they could clear the debris.
"That's the good part of our job, it's the exciting job," said Chuck Howlett, with Yentar Companies, which was hired to detonate the boulder. "There is no other reason to come out during weather like this."
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