DENVER (CBS4) – People lined up to see a piece of railroad history roll through Denver on Monday. The Union Pacific Railroad’s “Big Boy” No. 4014 steam locomotive, the world’s largest restored steam engine, made its way through Denver in the afternoon before the big snowstorm hit.

Union Pacific Railroad Big Boy No. 4014 in Denver, Colorado, on Nov. 25. 2019

Union Pacific Railroad Big Boy No. 4014 in Denver on Monday. (credit: CBS)

The engine has been touring the country this year to celebrate 150 years since the completion of the Transcontinental Railroad.

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“It was so big and it was so noisy,” said one little boy who watched the train go by.

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Union Pacific Railroad Big Boy No. 4014 in Denver, Colorado, on Nov. 25. 2019

(credit: CBS)

Robert Hill took his grandsons to see the train’s passing. It was everything they hoped for, and more. They only got to see the train for a few seconds, but he hopes its a moment that will last with them forever.

“I get joy out of it just watching that they get joy out of it,” Hill said.

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Union Pacific Railroad Big Boy No. 4014 in Denver, Colorado, on Nov. 25. 2019

(credit: CBS)

Big Boy will finish the tour on Tuesday when it moves from Denver to northern Colorado and then into Cheyenne, Wyoming.