Investigators believe alcohol, recent rain and reckless driving may have been factors in Friday night's crash of the Ford Bronco, which burned completely, state Trooper J.T. McMillan said.
"They were out there, playing around, mud-bogging on the dirt road," McMillan said. "They got stuck in the dirt and were pulled out by a dump truck. They sped off down the road and the driver struck two trees."
Mud bogging is an off-road motor sport in which drivers try to go as far as possible through a mud hole without bogging down.
The SUV was traveling around 70 mph at impact, and the occupants weren't wearing seat belts, he said.
Authorities say the deceased victims are Susanna Guffey, 24, who was driving the Ford Bronco; Christina Caldwell, 36; Guffey's 2-year-old son, Lucas Ross; and Zoe Jayde Flick, 4.
Guffey's four-year-old son, Brody, sustained minor injuries in the Friday night accident and was later released from Sylvan Grove Hospital in nearby Jackson.
Another passenger, Tammy Flick - the mother of Zoe - remains in stable condition at Atlanta Medical Center with a broken leg.
Neither is believed to have life-threatening injuries.
Griffin is about 37 miles south of Atlanta.