In recent years, genetic "fingerprinting" has revealed that Zinfandel is virtually identical to the Italian grape known as Primitivo.

It makes perfect sense that California and Italy would share a common grape variety, since many of California's earliest vintners were Italian immigrants.

By the way, both Zinfandel and Primitivo descend from a rare Croatian variety called (and good luck with pronouncing this!) Crljenak Kastelanski.