President Michael D Higgins has travelled to California to honour the victims of a balcony collapse that killed six college students and injured several others.
He met Berkeley's mayor, public safety workers, healthcare providers and area residents to thank them for helping when the balcony snapped off an apartment building.
Mr Higgins called the balcony collapse that happened during a birthday party on June 16 "a tragedy that has affected our people very deeply".
Five of the young people who died were from Ireland and working in the San Francisco Bay area for the summer.
"We were told and witnessed from afar your quick and unwavering support for our students and their families," he told a group of emergency service responders at a hotel close to where the balcony gave way.
Mr Higgins and Berkeley mayor Tom Bates shovelled dirt around a pair of strawberry tree saplings planted in honour of the victims in the corner of a city park near the Library Gardens complex, the site of the accident.
Mr Bates said the city council on Tuesday gave final approval to more stringent construction and inspection rules for balconies and decks that were a response to the tragedy.
"This event is not going to go unnoticed. It's not going to go down as a footnote in history," he said. "We are going to change the way we do business in Berkeley so it never happens again."
Five Irish students, all aged 21, and the 22-year-old Irish-American cousin of one of them died after the balcony gave way, tossing them and another seven young people celebrating at the party 50ft down to the street below.
A city investigation revealed that the wooden beams supporting the structure had rotted through from water damage.
The Alameda County district attorney has been conducting an investigation to decide if criminal charges are warranted.
Mr H iggins is on an eight-day West Coast visit that has already included a stop in Seattle, a visit to Google's headquarters and a speech on world hunger at the University of California, Berkeley.
The type of evergreen tree selected for the planting ceremony was picked because it is native to both Ireland and California.
The students who died in the accident were Olivia Burke, Eoghan Colligan, Niccolai Schuster, Lorcan Miller, Niccolai Schuster, and Eimear Walsh, all from Dublin.
The sixth, Ashley Donohoe, was from northern California but had dual Irish-American citizenship. She and Ms Burke were cousins.
Ms Donohoe's immediate family attended the ceremonies along with several cousins from Ireland who made the trip to honour both Ms Donohoe and Ms Burke.
Several of the seven Irish students injured in the collapse spent weeks undergoing surgeries and recuperation in the Bay Area, and the last to return to Ireland only left the US last month.
Irish consul-general Philip Grant said a few of them have gone back to their college studies.
One, Clodagh Cogley, was paralysed from the fall that severed her spinal cord, and another, Aoife Beary, suffered a severe head injury, he said.
Before the collapse, the Bay Area was the destination of choice for a large share of the Irish students who come to the US on summer work visas each year.
Mr Grant said it is too soon to know if the numbers will be down next year, but that he does not expect a change.
If anything, he said, "the bonds between the people of Ireland and Berkeley are even stronger".