"Carson passed away while trying to make others smile," Morley said.
Carson was just about to enter kindergarten, loved to ride his bike and was "full of life," said his grandmother, Geri Gibbs.
"There's still so much disbelief and sorrow and anguish," she said.
"We just keep waiting for the door to open up and Carson to come through, a happy little boy."
Gibbs said the boy and his family were visiting from Lehi. She said it took three men to pull the slab off the boy, and rescuers "did everything they could possibly do."
The child suffered injuries to his head, chest and abdomen and was taken to the nearby Park City Medical Center, where he died.
Morley works with the boy's father, Zac Cheney, at a professional services firm in Salt Lake City. He said Zac Cheney does photography in his spare time and was shooting portraits at the cemetery because of its extensive landscaping.
Park City Police Chief Wade Carpenter said the coarse stone at the Glenwood Cemetery in Park City, about 4 inches thick, marked the grave of someone who died in the 1800s.
Bruce Erickson, president of the Glenwood Cemetery Association, said the private, five-acre cemetery was founded by a society of silver miners in 1885, and many of the 900 tombstones are at least 100 years old. The cemetery is open to the public and still accepts burials of people connected to the mining society.
Erickson said no funerals were held there Thursday.
New burials happen about once a year, he said, and families are responsible for maintaining the headstones.
"I don't know where the family is, or if they even exist anymore," Erickson said. "We normally do not do anything with the headstones because they are property of the family."
Erickson said the cemetery likely will be closed through the weekend.
Carson's funeral is set for Tuesday at the Colony Pointe LDS Chapel, 1998 W. 900 North, Lehi. Visitation with the family is from 9 to 11 a.m., with the service to follow at 11:30 a.m.
A fund to assist his family has been established at Zions Bank in his father's name. Contributions to "Zac Cheney Donation" may be made at any Zions location.
Associated Press writer Lynn DeBruin and Tribune reporter Lindsay Whitehurst contributed to this story.