It represents us as a group, Mexicans, Latinos, said Jesus Ruiz, 16, a Salt Lake City resident.
Standing nearby, Sinyi Chua, 21, chimed in.
We love the flag, she said.
Through e-mails and fliers, the word had spread several days before the march that people were to bring American flags and wear white. The crowd had clearly taken the instructions to heart.
While there were some marchers carrying flags from countries such as Mexico, Peru and Honduras, the Stars and Stripes were dominant in the sea of participants, almost all of whom were wearing white shirts.
The shirts - ranging from tank tops to button-downs - were also part of the unity theme, although some marchers said it represented peace.
When Marcos Gonzalez, 15, walked from school to the Capitol during a recent protest, he carried a Mexican flag. Sunday he took turns with his family carrying a U.S. flag. To him, it represented his respect for the United States.
For Frida Gonzalez, 17, who was born in Virginia, carrying the flag was about showing her pride to be an American citizen.
The reason we have the flag is we're showing respect to the country of the dreams, she said.
Frida's sister, Yoshimi Gonzalez, 20, explained that having one flag was a way of symbolizing that immigrants could be from any country, whether it's El Salvador, Mexico or somewhere else.
We wanted people to know we're one, united as one, she said.