Winfrey spoke to the show via FaceTime from her home in their neighbourhood in the upscale hillside community of Montecito in Santa Barbara.
The Golden Globes winner said she did not realise the scale of the devastation until she put on her boots and waded through the mud in her yard.
The death toll has risen to 17 and more people are still missing after the mudslides caused devastation and destroyed 100 homes.
The scenic area of Montecito, which has been transformed into a mud bath, is located between the Pacific Ocean and the Los Padres National Forest.
DeGeneres yesterday shared an image of mud and fallen trees on the street outside her home on Twitter as the rescue work continued.
She tweeted: “This is the street in front of our house. I don’t know anything about our house yet.
“I’m heartbroken for our community of Montecito. I’m devastated for the families who lost loved ones. I’m grateful to all the rescue workers. Please send love to Montecito.”
On her talk show, DeGeneres said that the picturesque town of 9,000 is a “tight-knit” community.
“It’s not just a wealthy community, it’s filled with a lot of different types of people from all backgrounds,” she said.
“And there are families missing, there are people who are missing family members … it’s catastrophic.”
Ellen reportedly bought a property next door to Oprah’s, entertainment website TMZ reported last month.
TMZ said: “It’s in a gated community right next to Oprah. Ellen can literally go knock on her door for a cup of sugar.”