Fort Bend County Sheriff's Office said the incident happened Thursday night in the 1500 block of Fenn Road in Rosharon.
Officials say 74-year-old Maria Rico apparently tried to slide the gate open, but it somehow came off the track and toppled over on the woman. She may have been trapped for an hour or two before she was found.
Neighbors called 911, but the woman was pronounced dead at the scene.
The sheriff's office said the incident appeared to be accidental.