John Jones, 26, was part of a group of 11 experienced cavers who set out to explore the Nutty Putty caves, around 100km south of Salt Lake City, the capital of Utah.
Nearly three hours after the group had entered the caves on Tuesday evening, Mr Jones became stuck in a feature inside Nutty Putty, known as Bob's Push, the Utah County sheriff's office said.
"This feature is very tightly confined, being about 45cm wide and 25cm high,'' the sheriff's office said.
"Jones was positioned with his head downhill and was unable to move further into the cave. He was also unable to move back up the Bob's Push area."
Nearly 100 rescuers using large amounts of technical and heavy rescue equipment worked around the clock to try to free Mr Jones, who was trapped 46m underground and 213m from the entrance of the cave.
At one point they freed Mr Jones, but a rope and pulley system failed and he became stuck a second time.
Jones's brother, Spencer Jones, said: "We all were very optimistic and hopeful. But it became increasingly clear last night after he got re-stuck that there weren't very many options left.
"We thought he was in the clear and then when we got the news that he had slipped again. That's when we started to get scared."
Mr Jones lost consciousness late Wednesday, 28 hours after being stuck in the cave. Crews are still trying to remove his body.
His death is the first known fatality at the cave, according to the sheriff's office. Nutty Putty is now closed until a decision can be made about its future.
Spencer Jones said the family of five boys and two girls was close, and his brother was a wonderful person.
"He would have done anything for you, so that's what makes it even harder. It's senseless," he said.
Mr Jones leaves behind a wife and 8-month-old daughter.
Source: Adelaide Now