Thousands of people pack Civic Center Park in Denver to protest the detention of immigrant families on Saturday, June 30, 2018.

(Ann Marie Awad/CPR News)

Thousands gathered in Denver's Civic Center Park Saturday to protest the Trump administration's "zero tolerance" immigration policy.

The rally was one of hundreds of large gatherings across the U.S. urging the president to reunite families. Other, smaller rallies were held in Colorado, including in Glenwood Springs, Boulder and Durango.

In Denver, some wore foil blankets similar to those U.S. authorities have given to children they separated from their parents at the U.S.-Mexico border.

Emily Contreras, a University of Northern Colorado student, showed up to the rally with a sign that read: "We didn't cross the border; the border crossed us."

"I've had family members be deported," she said. "Last year, I barely finally got to see them. I just live with that fear that my family will be separated."

Nick Diaz held a sign that said "Who's the illegal alien, pilgrim?"

"All Europeans have one option we don't have," Diaz said. "If they don't like what's going on over here, and they don't like the political climate, they have one option indigenous people do not have. They can go home."

Other protesters held signs saying, "Keep the kids, deport the racists," and "Break walls, build families."

Joan Culwell of the city of Littleton said she had never been to a protest but decided to go after first lady Melania Trump recently wore a coat that read, "I really don't care, do u?" while traveling to visit migrant children.

Culwell wore a T-shirt saying, "I care!! Do you?"

Notable Democratic politicians made appearances as well, including Gov. John Hickenlooper and Denver Mayor Michael Hancock.

While the focus of the event was the policy of separating children from their parents at the U.S. Mexico border, other policies, like the Muslim ban, also came under fire. Forty-two immigrants who have been separated from their children are housed in a detention center just outside of Denver.

The Associated Press contributed to this report.