Authorities said it is a suicide, but did not say how he killed himself. An autopsy is scheduled for Monday.
A car matching the one driven by Ruelas was found parked near a bridge. His body was found below.
Ruelas' family became concerned when he failed to show up to work last week. He taught for 14 years and had nearly perfect attendance.
Friends and family said he was feeling stressed about work and a recent teacher evaluation report printed in the Los Angeles Times.
"He kept saying that there's stress at work," said Ruelas' brother, Alejandro.
According to his brother, Ruelas saw their sister Sunday and spoke with their father Monday night.
Alejandro Ruelas said his brother was a teacher who went above and beyond.
"UTLA is outraged at the Los Angeles Times," said A.J. Duffy, president of United Teachers Los Angeles in a statement. "We predicted there would be problems."
Duffy said UTLA will be working to, "implore the Times to pull the names of the individual teachers off the website now and to cease and desist from publishing any more in the future. "
In a response, the Times said, "We understand that the sheriff's department is currently investigating Mr. Ruelas death. We extend our sympathy to his family."