In Los Angeles, Mayor Karen Bass, Police Chief Michel Moore and others attended a remembrance in Elysian Park, at the home of the city's 9/11 memorial.
Among those also in attendance were first responders who were sent across the country to help with search and recovery efforts at Ground Zero in the days after the attacks. With national air traffic at a ground stop, about 100 firefighters from Los Angeles were able to hop on a military transport to assist at that time.
"Going for the first time to Ground Zero - smoke in the distance, cars stopped, people at checkpoints waving and saying thank you," said chaplain George Negrete with the Los Angeles Fire Department. "We hadn't done anything yet. So it was evidence of a response that we couldn't measure. The sound, the smell, the machinery working to try and rescue."
Former firefighter transforms yard of Fullerton home into 9/11 tribute
Retired Fullerton firefighter turns yard into memorial to victims of 9/11 attacks
Azusa 'Field of Glory' display honors victims of 9/11
Azusa honors victims of 9/11 with 'Field of Glory' display, ceremony
The centerpiece of the memorial in Los Angeles at the fire department's training center is a 23-ton steel column salvaged from the lobby of the collapsed south tower of the World Trade Center. The LA memorial was put up on Sept. 11, 2003.
9/11 Timeline: How the September 11 attacks unfolded
Some at the ceremony reflected on the degree to which the country came together in unity after the attacks.
"There was a really good thing that happened for about two years afterwards," recalled Dave Badgett, a retired LAFD assistant chief. "We collectively forgot our pettiness. We forgot that you like Fords and I like Chevys and all the rest of that nonsense that we get wrapped up on. And we all pulled together in one direction, and it was a wonderful thing. And somehow we've lost that."
Pepperdine University marks 9/11 with 3,000 flags in honor of lives lost
Pepperdine University marks 9/11 with 3,000 flags in honor of lives lost