Here’s a picture
I took these pictures in my back yard in Pacifica, CA. (since you ask for a better one than on your site) Thanks for telling us that they were the black swallowtail. They were on a Fennel plant but did not cocoon there… Blessings,
Black Swallowtail Caterpillars and Anise Swallowtail Caterpillars look very similar. Black Swallowtails are found in the Eastern U.S. and Anise Swallowtails in the West. Your caterpillars are Anise Swallowtails.