Participants from Utah, Arizona, Idaho and elsewhere gathered in a public park to sign a "Declaration of Independence from Mormonism."
"This feels awesome," said Alison Lucas, from West Jordan, Utah, who took part in the rally amid soaring temperatures. "I don't know if I would have had the courage except in a group."
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.