A passerby saw the 1960 Studebaker, the (Sioux Falls) Argus Leader reported. Investigators say it belonged to Sherri Miller's grandfather.
Miller and Pam Jackson, both juniors at Vermillion High School in Clay County, were last seen on May 29, 1971, in the Studebaker. Classmates said they were trying to find a party in a gravel pit located about half a mile from the place where the car was discovered under a bridge in Brule Creek in Union County, which neighbors Clay County in South Dakota's southeast corner.
Attorney General Marty Jackley and Union County Sheriff Dan Limoges said water levels in Brule Creek had dropped to a record low, leading to the discovery.
The investigation into the disappearance was revived in 2004. A convicted rapist who lived in the area in 1971 was charged in 2007 based on a supposed prison confession, but the charges were later dropped.
"This case isn't about him," Jackley said when asked about David Lykken. "It's about finding what happened to two young girls."
Jackley said the Department of Transportation tried to get the Studebaker out of the creek and decided it was too badly damaged to be moved immediately.
Limoges and Jackley would not say if the girls' bodies had been found.