STEAMBOAT SPRINGS, Colo. (CBS4) – A second person has been cited for “rolling coal” at demonstrators a March For Our Lives event in Steamboat Springs on Saturday.

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“Rolling coal” happens when a driver lets out large cloud of exhaust – typically among truck drivers.

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That act is illegal under Colorado law.

The exhaust covered a crowd participating in a March for Our Lives event, which was one of hundreds across the country.

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(credit: Camille DiTrani)

Witnesses say truck blasted the marchers more than once.

Alex Graham, 20, was cited by police on Sunday after witnesses turned in a picture of the truck he was driving.

(credit: CBS)

Police say they cited a second driver, Mitchell Klouw, who is an 18-year-old high school student from Clark, Colorado.

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Police say they’ve identified a third vehicle involved, and they are working to track down that driver.