The Utah-based Church of Jesus Christ of Latter-day Saints is known for its culture of obedience, and the mass ceremony was a seldom-seen act of collective revolt.
After gathering in the park, participants hiked a half-mile up nearby Ensign Peak, scaled in 1847 by church President Brigham Young to survey the spot where his Latter-day Saints would build a city.
At the top, those gathered gave three loud shouts of "Freedom," cheered, clapped and hugged.
"It's been a hard journey and this is a symbolic end," said event organizer Zilpha Larsen, of Lehi, Utah. "I just hope that it boosts people up and helps them feel more comfortable in their decision."
The church bills itself as the one "true" Christian faith, and its theology promises families eternal relationships among those who remain faithful, sealing those gifts through special religious rites.
Among the reasons cited by those resigning are the church's political activism against gay marriage and doctrinal teachings that conflict with scientific findings or are perceived as racist or sexist.
Others cite inconsistencies in the Mormons' explanation of its own history, including the practice of polygamy. The church renounced plural marriage over a century ago as Utah was seeking statehood.
Asked about the resignations, a church spokesman said the church loves and respects each member.
"People make their own decisions about the direction they will follow in life," spokesman Michael Purdy said in an email. "While there are very few who take this action, it is sad to see someone choose to leave. We wish them well."
The most recent figures show the Mormon church claims 14.4 million members worldwide. The number of those resigning from the church are not publicly reported.
Among prominent Mormons is Mitt Romney, the presumptive Republican presidential nominee facing off against President Barack Obama in November. Should he win office, Romney would be the first Mormon elected to the White House.
Some leaving the church Saturday did so with trepidation, as Mormon culture often stigmatizes those who fall away, leaving some without social or business connections.
"It's hard, so we have to be very careful," said Robin Hansen, a participant who said she quit over a "culture of abuse" which she believes is cultivated by church teachings promoting obedience.
Hansen said her husband had not joined her in leaving the faith because he works in a church-related business and could lose his job if he doesn't maintain his membership.
To resign from the church, Mormons must submit a formal letter asking their names be removed from church rolls, a church instructional handbook for lay leaders published on the Internet in 2010 shows.
On Saturday, participants filled a basket with their letters for mailing by Larsen, who split with the church over doubts about the veracity of a translation of ancient Egyptian writings which are included in sacred Mormon texts.
A sixth-generation Mormon, Kris Fielding, 35, traveled from Phoenix for the resignation event in part to represent those who do not yet have the courage to do so, he said, including his wife, who worries about reaction from their families.
Married in a Mormon temple, Fielding said the couples shared disaffection from their faith is tied in part to their local church leader's response to questions Fielding had about polyandry and polygamy - taking multiple husbands and wives - in the early church.
"I went to him looking for a faithful perspective. He called my wife and told her she needed to find a new husband," Fielding said.
He said he felt relief after his decision.
"The monkey's off the back ... I don't feel like I have to explain myself or the positions of the church anymore."
(Editing by Tim Gaynor and Doina Chiacu)