The zoo confirms that Iringa, Toka and Thika were loaded into their individual steel crates Thursday and then began their journey by truck — expected to take about 50 hours.
Four staff members who have been working with the elephants and assisted with the loading are travelling with the convoy as it heads to the Performing Animals Welfare Society Sanctuary.
The trucks left the zoo Thursday at about 10:30 p.m., after a day of delays and zoo officials say the convoy crossed the U.S. border around 5:30 a.m. Friday.
Toronto city council voted in 2011 to send the three aging elephants to the PAWS sanctuary near Sacramento after animal rights advocates voiced concern for their welfare.
The zoo says staff members worked with a team from Active Environments, the group managing the move, to make sure the elephants were loaded safely onto the trucks for transport.
"We wish the elephants and everyone travelling with them a very safe journey," the zoo said in a statement Friday, adding the loading process was "a very emotional time" for staff.