Isabel Grace Franks was sitting inside the hole when it collapsed, burying her. She was under the same for five minutes before she was pulled from the sand unconscious and not breathing.
Witnesses said the sand kept refilling the hole as rescuers tried to dig Isabel out.
"Well the people were digging," said Tracey Dudley, "and digging and digging, and it looked like the sand kept collapsing."
Emergency crews attempt to perform CPR on the girl, but she was later declared dead at Samaritan North Lincoln Hospital.
Witnesses told KATU-TV the girl had been digging the hole with her siblings and friends when she got down into it to see how deep it was. Observers said the hole was big enough for an adult to crouch down in without being able to see above the top.
Mourners made a makeshift memorial with flowers, candles and a wooden sign at the spot where Isabel was digging on the beach.
This is a makeshift memorial where a 9 year old girl died when sand collapsed on a hole she was in. pic.twitter.com/0L7Jf9wZ0c— Wayne Havrelly (@HavrellyKGW) August 30, 2014