Trisha Graf, aged 41, was last observed in the vicinity of Roxby Downs nearly a month ago. Her Ford Territory was discovered deserted to the east of Andamooka on the day she disappeared.

Graf had spent time with friends at the Roxby Downs hotel until around 12:30 a.m. on Friday, December 12.

During their journey home, the pair collided with a kangaroo not far from the Andamooka township.

Following the collision, Trisha and her companion proceeded to Andamooka, where they visited a residence in the town’s north-western area.

Graf departed at 2 a.m. to travel a short distance home and was last witnessed driving on Dunstan Drive.

Her vehicle was located abandoned near Blue Dam shortly after midday.

“This is highly unusual and particularly out of character for her,” South Australia Police detective superintendent Darren Fielke said.

“The dam has been searched by police divers, polair has been involved in aerial searching and we’ve also utilised specialised drone equipment,” Fielke said.

“Police have spoken to a number of people and in Roxby Downs who have assisted piecing together the movements of Trisha.”