In the southern Rhône, the practice of blending grapes is raised to a high art.... and Grenache is given pride of place, with Syrah and Mourvedre playing supporting roles (thus the term, "GSM blend"). This tradition is even codified as law in France, wherein if you want to get to brag about your zipcode (Chateauneuf-du-Pape, say) you've got to abide by that zipcode's rules.
But here in California? There's no governing appellation making a priori decisions about what goes with what, in what quantities -- so instead of dutifully adhering to a regulatory framework, winemaking team Jason Lefler and Aaron Jackson were free to improvise, and Oh Mama are we happy they had their freedom. They quickly intuited that Syrah was their gemstone, and (extending that metaphor) enlisted other grapes as the jewelry in which to set it.
The Syrah provides a core of plum, cherry, violet and bacon. The Grenache fills in the mid-palate, and adds a mineral note; the Mourvedre provides a little bit of baked fruit and some tannic structure. And lastly (sorry Chateauneuf, but we have some things you don't!), they added a very small amount of Petite Sirah to lengthen the finish. The resultant wine is a multi-dimensional and age-worthy wonder, and one that evolves with every hour it's open -- you can’t sit with this in your glass and not stop and whistle a bit. One of the best wines the Stereophonic team has ever made.