While family and friends are still in shock after Saturday night's crash, authorities are still trying to piece together what happened.
The Highway Patrol says troopers are actively investigating and reconstructing the scene to find out exactly what happened moments before the Vollmer family SUV left the road.
"Our hearts go out to the family during this difficult time," South Dakota Highway Patrol Captain Kevin Joffer said.
Highway Patrol says around 5:15 p.m. on Saturday, Jim, Julie, Alyssa and Caleb Vollmer were heading east bound on I-90 when their family SUV left the road and hit a cable guard. The 2005 Ford Expedition Sports Trac then hit and vaulted off an embankment and landed in a gully.
"As a result of that crash, three members of the Vollmer family were killed in the crash. And then Mrs. Vollmer was air lifted to Sioux Falls, where she later succumbed to her injuries," Joffer said.
Authorities say all four members of the Vollmer family were wearing their seat belts. Highway Patrol says they are looking into anything to find a cause.
"We have a family out there too, that at some point I'm sure, they would hope to know or want to know so we want to do everything we can to determine the cause of this," Joffer said.
Joffer says he does not believe icy road conditions were a factor in the crash. He says with such a tragic event, the Highway Patrol will investigate until they find what caused the SUV to veer off the road.
“We do these fatal crashes more than we would like to. It isn't so much speed, but being accurate and we chase down whatever leads that we have," Joffer said.
The Highway Patrol is looking for witnesses. If you were in the area Saturday night, you're asked contact the Highway Patrol.