"This was supposed to be a 15-minute stop with about 20 people," said the Illinois senator, dressed in slacks and shirt sleeves. "Somehow this grew a little bit."
Said Doug Gray, of Taylorsville: "If he can get this kind of turnout in Utah, imagine what he can do in the rest of the country."
Obama had planned a brief stop before attending a private, $500-per-person fundraiser reception in Park City and then a rally in Elko, Nev. When his motorcade of six black SUVs pulled into the parking lot near Kimball Junction, the crowd cheered with shouts of "We love you, Obama."
"I love you back," shouted Obama, who seemed surprised by the turnout in a Republican stronghold state.
Yet the sole black candidate has become accustomed to drawing large crowds, speaking to thousands of supporters in Atlanta and Austin, Texas.
"I like to think it's because I'm so fabulous," he joked. But the real reason, he said his wife has reminded him, is that Americans are discouraged with the nation's direction.
"The country is ready for change," he said. "People want to turn the page and start a new chapter in history."
In a 20-minute speech, Obama touched on health care for all Americans, better pay for teachers and, of course, the war in Iraq. Obama also defended himself against attacks on his lack of experience.
"I find it amusing when the people who are responsible for engineering the biggest foreign policy fiasco in our generation are giving me lectures about being naive," he said.
As for criticisms of his alleged naiveté when he said he would be willing to talk to any nation, Obama said that if Americans are clear about the nation's values and interests, "then we should have no fear of losing a propaganda war with dictators."
Obama also stressed a recent campaign theme that - unlike poll leader Sen. Hillary Clinton, who accepts money from lobbyists - he is an outsider who can bring change.
"If you don't think that the oil companies and the drug companies have disproportionate influence in Washington, you've been in Washington too long," he said. "You're part of it."
Finally, Obama hit on the core theme of his campaign: Hope.
"When I talk like this, people in Washington, they get cynical," he said. "They say, 'He's talking about hope again. He's such a hope peddler. He's a hopemonger.' "
Before jogging up to the crowd to shake hands, Obama said, "I stand guilty as charged. I'm hopeful."
Steven Harper, who drove from Salt Lake City to a Denver rally to get an autograph on Obama's book, Dreams From My Father, added a signature Sunday to the senator's memoirs, The Audacity of Hope.
"Americans finally have a serious candidate," said Harper.
Another face in the crowd was Pete Ashdown, unsuccessful Democratic candidate for Utah Sen. Orrin Hatch's seat. Ashdown said he hasn't decided which Democratic candidate he will support.
"I like Barack," said Ashdown. "He's outside the establishment and he's indicative of the Democratic Party's inclusiveness."
Even after most of the crowd had left Sunday, Obama was still pressing hands and signing autographs.