SIOUX FALLS - Neighbors say they're heartbroken over the fiery wreck that killed a Sioux Falls couple and two of their children.

James and Julie Vollmer died Saturday in a one-vehicle crash west of the city on Interstate 90. With them were their children, 16-year-old Alyssa, and 13-year-old Caleb. The family leaves behind a daughter, who was away at college.

Neighbor Tammy Klein tells the Argus Leader the Vollmers were the first people she met when she moved. She was hauling her belongings off the moving truck when the Vollmers swept her away to a Fourth of July party.

Sioux Falls Christian Superintendent Jay Woudstra tells KELO-TV the parents were "salt of the earth."

Investigators say the victims were wearing seat belts and alcohol wasn't a factor. The wreck's cause is under investigation.

Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.