Mum's 'suspicious' disappearance declared a major crime

Police are treating the disappearance of Trish Graf as a major crime. (HANDOUT/SOUTH AUSTRALIA POLICE)

The disappearance of a mother of two has been declared a major crime, three weeks after her car was found abandoned at a remote outback location.

South Australian Major Crime detectives have outlined the last known movements of Andamooka woman Trisha Graf, 41, whose Ford Territory was found perched on a dirt mound near a dam on December 12.