The Rimouski fire department said more than 20 firefighters and emergency workers spent several hours trying to reach the woman, who was transferred to hospital with serious back and neck injuries.
Quebec provincial police said the woman fell into the ravine by her home at around 9 a.m. yesterday.
A friend became alarmed after she couldn't locate elderly woman, who lives alone, inside or outside her home near the ravine.
The friend said she walked around the property and spotted the 100-year-old woman on the ground at the bottom of the ravine, not far from the fast-flowing water.
Emergency crews were called to help just after 3 p.m.
Bertin Santerre of the Rimouski fire department said rescuers had to make a path through the woods to reach the woman.
"We deployed the rescue team, who did a tremendous job stabilizing the person," he said.
The woman remains in hospital in Rimouski.