Despite what many people seem to think, Syrah and Petite Syrah are not the same grape, although a geneticist would say they have a shared ancestor. Petite Syrah is generally considered native to California, although it is very possible that this grape is simply a Syrah grape which was being grown in more difficult conditions, leading to smaller grapes and bunches, possibly leading to the Petite being added to the name.
Over the years, especially when starting when the grape was truly discovered in the 1880’s, bad vineyard management policies lead to multiple grape varietals being comingled together. UC Davis has pioneered genetic testing of grapes and they have discovered that Petite Syrah is actually a genetic variety which is a combination of three different unique grapes. It is usually some combination of Duliff (a French cross of Syrah and Pelosuin) Syrah and Grenache, Barbera etc. It is this sense of mystery that adds to the cult like personality of Petite Syrah.
When made well, this California varietals comes off as a massively huge wine that can be largely rustic and an amazing pairing with BBQ meat and other heavy meats.