The mother of a missing nine-year-old girl has been arrested on suspicion of murder after her daughter was found dead in Utah, police have said.

Melodee Buzzard's decomposed body was found by a man and woman who were taking pictures in a rural area of Utah, earlier this month.

Her 40-year-old mother Ashlee Buzzard was taken into custody on Tuesday and is being held on suspicion of first-degree murder, the Santa Barbara County Sheriff's office said.

Melodee Buzzard had been missing for months and investigators said her mother had not been cooperating with the investigation.

"This is an extraordinarily tragic case involving the murder of a child by the very person she relied upon and trusted the most," Santa Barbara County Sheriff-Coroner Bill Brown said in a statement.