San Diego Humane Society said the kittens wound up inside a 60ft steel column that travelled on a truck from Hayward in the San Francisco Bay area to San Diego.
On April 24, construction workers building new Kaiser Permanente medical offices heard meows coming from the column.
They tilted the column and the week-old kittens slid out.
It was unclear whether the stowaways got aboard in Hayward or somewhere along the route.
The kittens are now in foster care and will be ready for adoption in a couple of months.
They have been given appropriate construction names: Crowbar, Rebar, Chisel, Jackhammer and Piper.