She was Betty Rubble

Voice actors are usually never given a second thought. One of the most instantly recognizable voices is that of Bea Benaderet. Bea played not only the owner of The Shady Rest Hotel on "Petticoat Junction" and she also was Jethro's mother on "The Beverly Hillbillies". She is always going to be remembered as the voice of Betty Rubble the Millis Helper of the "The Flinstones".

Benaderet  had a long career on radio where she was able to develop her voice. On Radio she was a star during rodio's hey days. When television emerged Bea not being a fool knew this was the way to go, the wave of the future and jumped into it. Bea was originally supposed to be Ethel Mertz on "I Love Lucy" having done a very similar role on the radio version "My Favorite Wife".
Her work in cartoons wasn't only limited to to betty Rubble she was also the voice of Granny in the Warner Brother's cartoons with Tweety Bird. 
Bea Benaderet died in 1968 of lung cancer, she was 62 years old and in the height of her career.