An officer found her about 8 a.m., 30 minutes after her mother reported her missing.
An autopsy showed her death was a homicide and determined she was sexually assaulted, police say.
Investigators have no suspects, and West Jordan Police Chief Doug Diamond has cautioned residents that "there's obviously a predator out there."
He urged the public to lock doors and windows and watch children carefully when they are outside.
Patrols have been increased near the Newbolds' home as a precaution.
A vigil was held Friday at Sierra's school, West Jordan Elementary, and her funeral was Saturday.
"We are most grateful and deeply moved," her father wrote, "by the public outpouring of support during this tragic time."
Police have confirmed that surveillance video at the Newbold home captured images, but they declined to elaborate.
They also would not discuss how long Sierra had been dead before police found her body, the cause of death, how she might have ended up in the canal and if they recovered DNA evidence.
"I plead with anyone who has information about the death of my daughter to please call the West Jordan Police Department," Brad Newbold wrote.
Investigators can be reached at 801-256-2211.
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