The couple, who live about 145km north of the city, were seen at the Pasadena Convention Centre on Friday, handing out food and supplies alongside other volunteers.
During their visit, they met Pasadena Mayor, Victor Gordo, and thanked first responders for their efforts amid the catastrophic fires, which have claimed at least 11 lives and destroyed more than 10,000 structures so far.
The Duke and Duchess of Sussex also met chef and World Central Kitchen founder José Andrés at the food stations to thank the relief teams.
“It’s great people, great personalities and great heart for them to come out here and meet with the first responders, meet with the people who were affected,” Gordo told Fox 11 of his meeting with the pair.
Gordo added that their visit “really buoyed the spirits of the first responders” and that “people were very happy to see them”.
“They want to be as helpful as they can be … we visited with some of the affected families in some of the burnt-out areas in Pasadena and Altadena,” he said.
“They took the time to meet the people that are affected and spent time. They’re just very caring people who are concerned for their friends and neighbours.”
Gordo explained that the high-profile couple had visited the World Central Kitchen “anonymously” by “serving food with masks” and wearing baseball caps.
He also insisted that Harry and Meghan weren’t there for “publicity”, but were keen to “work”.
“We went to visit some of the families in the impacted area and view first-hand some of the impacted area and then they wanted to go visit the first responders and personally thank them for their efforts to help our families and their neighbours,” Gordo said.
The outing comes after Harry and Meghan released a statement on the “apocalyptic” wildfires that have decimated the area.
“In the last few days, wildfires in southern California have raged through neighbourhoods and devastated families, homes, schools, medical care centres, and so much more – affecting tens of thousands from all walks of life,” the message on their Archewell website read.
“If a friend, loved one, or pet has to evacuate, and you can offer them a safe haven in your home, please do.”
It’s understood the couple have opened the doors to their 16-bedroom mansion to friends who have been forced to evacuate, and have also donated to relief funds through the Archewell Foundation.