I'm rusty.

Yes, I am blog-rusty, but not as rusty as this chunk of tuff situated underneath a drip irrigation emitter.  Stained a curious shade of orange, from the iron present in Vinoland's well water, this fractured hunk of ash-fall tuff distracted me from the job at hand.  (For more on tuff, see here.)  I've been keeping busy stuffing shoots, thinning heads and suckering trunks.  And watching this California Harvester Ant (Pogonomyrmex californicus) bopping around under a Syrah vine, fascinating.  I'm easily distracted.  Situation, normal.

Once upon a 160 million years ago.

One hundred and sixty million years ago today the Napa Valley was underwater.  Not underwater as in the my-mortgage-has-a-higher-balance-than-the-market-value sense. No, the Napa Valley was literally underwater. Glug, glug.
I had the honour of spending yesterday evening in the rarefied company of a multitude of Oakville winegrowers and vintners: a veritable who's who of the Oakville AVA.  The Oakville Winegrowers were hosting geologist David G. Howell at the Robert Mondavi Winery and I was fortunate enough to be extended an invitation to attend.  Yay!  Once again, Mr. Howell's insight as to the geological history of the Napa Valley, specifically Oakville, and its influence on present-day grape-growing was riveting stuff. God bless vulcanism, plate tectonics and glaciation.
Aside from the 160 million year geological-education, I was given the opportunity to sample a plethora of Oakville wines, mainly from the 2012 vintage, prior to the presentation beginning. Really fascinating stuff, the presentation and the wine.  All of the attendees had contributed bottles of their own wines for the pre-presentation meet-and-greet.  I have to say, of all the wines represented, the TWWIAGE Cabernet sauvignon really stood out from the crowd.  That made me very happy.

Tuff stuff.

A small excavation in Vinoland has revealed a friendly, neighbourhood igneous rock (everybody should have one).  Tuff, or ash-fall tuff, is extremely variable in its chemical and mineralogical composition.  Vinoland's tuff happens to be extremely light in weight and texture, but there exists some historical references (The Structural and Industrial Materials of California, Bulletin No. 38, State Mining Bureau, 1906), to a brecciated tuff, mined just a mile or so from here, that "...for many years has been used for macadamizing the streets of Napa."  Now, that's tough stuff.
Tuff is a fine grained rock composed of volcanic ash which fell upon this part of the Napa Valley millions of years ago, (vulcanism reached the valley about 7 million years ago), which later hardened into beds of tuff.  Vinoland's tuff is really light in colour (it resembles diatomaceous earth in appearance, though it is denser), includes no clasts (volcanic detritus), rubs off on your fingers like chalk and is usually high in silica. 
Tuff is only found in a small area in the south end of Vinoland, (some Syrah is planted in it, tough stuff for a grapevine to deal with).  I know that at least one of our neighbours over the hill behind Vinoland has a large amount of it, but I don't know how extensive it is in the neighbourhood as a whole.  Some folks claim that the volcanic rock in the Napa Valley is responsible for certain characteristics in the grapes and resulting wine.  However, due to the huge diversity in the types of volcanic rock deposited in the length and breadth of the valley, I am of the opinion that there is little significance you can attribute to just one specific lithology.

Geology matters!

Yes it does, especially when it comes to explaining just why the Napa Valley is such a unique place to farm wine grapes.
Today, I had the pleasure of meeting one of the co-authors of my favourite book on the complex geological history of the Napa Valley: The Winemaker's Dance by David G. Howell.  Y'know, if plate tectonics and other such earth moving events are your thing, this is a great read.  Like some geeky rock (get it?) groupie, I could feel myself blushing the entire time that Mr. Howell chatted to me (about Coombsville) and signed my copy of his book.  Haven't been that excited since I met Johnny Thunders.
Let the good times (rock and) roll!