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Snooth User: Gregory Dal Piaz

What Were Why - Napa Valley's AVAs

Posted by Gregory Dal Piaz, Oct 30, 2008.

By far the most famous appellation in California, and for that matter in the USA is the Napa Valley. Encompassing virtually all of Napa County as well as 14 distinct AVAs (American Viticultural Area), this extensive valley system, about an hours drive north of San Francisco, is home to the cradle of California’s viticultural history. While Cabernet is king in Napa each of the AVAs was recognized for the specific qualities that made it a distinctive region for the grapes best suited to it’s micro-climate and soils.

Napa Valley opens to the south where the climate is heavily influenced by the maritime influences of the great San Pablo bay. This regular influx of cool, damp air creates a meso-climate that is significantly different from that of the Northern reaches of the valley where a days heat can remain trapped and accumulates over the course of the summer growing season.

The other great influence on the climate of the valley is the mountains that frame it’s contours. With the Mayacamas Range separating Napa from Sonoma on the west and the Vaca range defining the valley’s eastern boundary there are many varied exposures, elevations, and soils here that have been deemed worthy of special attention.

What follows is a rough run-down of the Napa Valley AVAs roughly from South to North and then back again.

Los Carneros- The first AVA one comes to as one splits off the Napa Vallejo Highway and takes route 29 towards the City of Napa from the south is Los Carneros. Reaching from close to the southern border of the county to the southwestern edge of the City, Carneros was the first AVA to be determined solely by climate. It has the unusual honor of spanning across the southern reaches of both Sonoma and Napa counties.

The climate here is cool, think summer in San Francisco, and while the average rainfall is the lowest in Napa Valley it can be a humid region due the fog that rolls in off the bay. These conditions are ideal for the so-called cool climate grapes of Burgundy. Pinot Noir and Chardonnay rule the roost here yielding ripe yet balanced wines with fresh acidity and a round, friendly feel. Merlot is a distant third, though the cool, crisp quality of the fruit can produce attractively elegant examples and an excellent structural component for blending.

Los Carneros is a source of successful sparking wines from Napa valley that benefit from the high acid, cool climate fruit grown here.

Mount Veeder - Directly to the North Of Los Carneros and veering off to the Northwest for some 13 miles as it follows both the Mayacamas range and the boundary with Sonoma is the Mount Veeder AVA. It is here that one finds the steepest, most challenging vineyards in Napa Valley.

Based as it is around the slopes of a long dormant Volcano, Mt. Veeder's soil is composed of decomposed basalt and compact ash as well as sandstone and shale at the lower elevations. With almost 3 feet of rail annually, these porous soils are one of the elements that distinguish this AVA, no to mention making it even more challenging to establish a vineyard here.

The high elevation, ranging from 600 to 2300 ft, keeps the vineyards out of the reach of the San Pablo bay fog and results in temperatures that are moderate for the region. This combination of factors creates some stern, structured wines but with beautifully complex fruit.

Cabernet and Chardonnay long have been the grapes of note from Mt. Veeder, with the Chardonnays retaining bright acids and a minerally character and the Cabernets yielding very powerful yet balanced wines with exceptional cellaring potential. In the past some excellent Zinfandels were produced here but more and more Syrah is usurping that second level position. The meager soils here and conditions that foster small berries have produced powerful yet minerally Syrah that is quite distinct from the fruit driven versions more commonly encountered in the region.

Spring Mountain District - Further North but with a similar situation one finds the rather broad ranging Spring Mountain District. With cooler daytime temperatures than Mount Veeder, these slopes range with-in the same elevations but their positioning results in almost twice the annual rainfall of Mount Veeder. As the air in Napa Valley warms and is drawn to the north, warm, moist air is drawn through a gap in the Mayacamas Range resulting in regular, cooling rainfalls. Not actually a mountain, this region is more of a broad high pass that straddles this gap between the Mayacamas and Diamond Mountain.

These same air flows often contribute to evening fogs in the valley floor to the East which results, counter-intuitively, in warmer evening temperatures at higher elevations as this blanket of cool, damp air forces the warmer air up the slopes and into the valleys of the district.

The production of the Spring Mountain District is modest, contributing a mere 2% to the Napa valley Total. With soils similar to the volcanic, seafloor influenced types found in the Mt. Veeder AVA the wines tend to share a similar character though the temperature differences tend to yield softer, rounder wines with a bigger fruit impact, though with similar ageing potential. Cabernet is, not surprisingly, the predominant variety for the region.

Diamond Mountain District - Adjacent to the Spring Mountain District and just to the north is the Diamond Mountain AVA. Soils here are even poorer than to the south with very little ability to hold moisture and very low heat retention. They have a bit more iron than is usual for the region and are very loose and rocky yielding wines that tend to be a bit more austere and even minerally.

Like the other mountain AVAs there is little problem with the fog so typical of the valley, resulting in a long growing season and a compressed range of daily temperatures as daytime highs are moderated by the cooling airflow of these high elevation slopes and nature of the soils while nighttime lows are moderated by the heat given off from the valley floor to the east.

Long hang time is a factor here as the season extends from March to November. The Cabernet is justly famous for it’s combination of power, complexity and elegance. As with the Chardonnay the wines tend to be leaner than the Napa Valley benchmarks, revealing the character these conditions impart in the wines.

Calistoga - This northern most AVA isn’t an AVA yet. The petition to create the Calistoga AVA is still pending but this northernmost reach of the Napa valley floor and foothills north of Diamond Mountain certainly deserves the recognition.

Being both the northern most reaches of the valley as well as surrounded on three sides by foothills, Calistoga enjoys the warmest position in all of Napa. The moderating maritime influences that affect most of the valley are rarely encountered here and while the proposed AVA includes both valley floor and hillside vineyards, the warmth here tends to have a universal impact.

Wines from the area tend to emphasize big, bold fruit and are prone to notes of over-ripeness. This is the area for big, jammy Zinfandels and full throttle fruit driven Cabernets, both Sauvignon and increasingly Franc. Chardonnay does well here though it is generally of the rich, buttery style best suited for the fruit of such a warm zone.

Howell Mountain - Unlike the pending Calistoga AVA the Howell Mountain AVA not only exists but also was the first AVA to be carved out of the Napa Valley appellation, way back in 1984. Roughly centered around the town of Angwin and stretching north to south some 12 miles or so, it roughly parallels the range of the Diamond and Spring Mountain districts

This western facing AVA hugs the Vaca Mountain range that forms the eastern edge of the valley and benefits from the long hours of afternoon sun it receives. The great exposure of the vineyards is more important here than anywhere else in the valley as these rolling vineyards, concentrated between 1200 and 2200 feet above sea-level, are surprising cool, with daytime highs frequently 10 degrees lower than the valley floor. These lower temperatures lengthen the growing season and allow for valued hang time. The key to the wines here is the slowed down maturation cycle which allows the grapes to ripen in tune with the tannins, and yet retain naturally balanced acidity.

The name Howell Mountain gives a somewhat misleading impression for this area is really more of a high plateau as opposed to the vertiginous vineyards of Mount Veeder. As with the western mountain AVAs the soil here is volcanic in origin and offers excellent drainage, though the region is dotted with picturesque lakes. The area remains mostly wooded with only several hundred acres devoted to vines but the wines that are produced here are perhaps the most distinctive in the valley.

The terroir of Howell Mountain is quite assertive; these are lean and earthy wines if judged against most from Napa Valley. The soils here are very poor and the vines fight for their lives. The stresses the vines face and the well-drained soils yield small, intense grapes that translate into these distinctive wines, massively structured and speaking of the dirt from which they’ve come. This should not be mistaken for a lack of fruit however. These wines are well endowed with perfectly ripe fruit, and perfect balance. They just lack the jammy edge many wines from Napa exhibit and have replaced it with compelling layers of mineral and savory flavors.

Many grapes do very well in this mild climate, and while Cabernet remains the most prominent, brawny and powerful with deep fruit and imposing structure, it can be argued that the stars here really are the rich, spicy Zinfandels, the fully ripened, deep Cabernet Francs and the powerful, structured Merlots, as they tend to be the best one will find in the Valley.

Chiles Valley - If one continues into the Vaca Mountains to the east of Angwin one comes to Chiles Valley. This long thin valley is as removed from the heart of Napa valley as one can get and stay in the appellation. Being isolated from the moderating breezes of the maritime west, and having fairly well defined and closed valley walls means that Chiles Valley sees significant heat accumulation during the day though the 800 to 1200 foot elevation keeps even summer evenings cool.

While summers may be warm in Chiles Valley the springs tend to be cool and the flowering of the vines general lags the rest of Napa by a week or two, leading to later harvest that can take advantage of the falling autumn temperatures, thus ameliorating the heat of summer to a degree.

The cooler fringes of the valley are well suited to Sauvignon Blanc and the standard trio of red grapes, Cabernet Sauvignon, Merlot, and in particular Zinfandel do very well here in the rich, alluvial soils of the valley floor, where the vineyards lie, producing big, lushly fruited wines that can seem far different from the wines of the Napa Valley bench lands and hillsides.

St. Helena - Just to the south of Calistoga one comes to St. Helena. Sharing much the same features as Calistoga, St. Helena is a warm region, benefitting from the narrowness of the valley here and its limited exposure to the maritime influence of more southerly AVAs. Temperature swings between day and night, (Diurnal shift) are pronounced here frequently exceeding 30F. This allows for the grapes to easily achieves ideal ripeness while retaining bright, natural acidity.

This is a true valley floor AVA and the soils here represent a transition from the decayed volcanic material found in the north to the sedimentary clays and bands of gravel that makes up the majority of the southern half of the region. This relatively flat area ranges roughly between 600 and 150 feet in elevation and opens to the broad plain of Napa Valley to the south.

St. Helena represents the northern end of the broad valley floor and it is here that the Silverado trail veers towards the eastern side of the valley offering wine travelers two distinct routes for travelling North to South through the valley.

Cabernet remains king here but faces some tough competition from great Zinfandel and Petite Sirah as well. The cooler hillsides produce fine Sauvignon Blanc, which are much more common than Chardonnay here. Emerging varieties such as Syrah and Cabernet Franc have also found a home in this ideal, and flexible AVA. The combination of warmth days, cool nights and varied soils allows for wine to be rich and ripe yet layered and complex with very fine tannins.

Rutherford - Just to the south of St. Helena lies Rutherford, the historic home to the old Inglenook estate and Beaulieu Vineyards and arguably the greatest spot in the country to grow Cabernet Sauvignon, though I will argue with this proposition in just a minute. Rutherford has even spawned perhaps America’s only contribution to the lexicon of wine tasting, the mysterious “Rutherford dust”, that dusty, dusky note that can merge in old California Cabernet.

Rutherford occupies the heart of the Napa Valley floor. Roughly square shaped the area is at the crossroads of the valley, benefitting from some maritime influence and fog yet enjoying moderately warm average daily temperatures. There are distinct differences however between the Eastern and Western halves of the AVA.

In the west the valley floor is shaded by the Mayacamas range, resulting in cooler afternoon temperatures as well as less fog in the morning. The soil here is predominantly volcanic runoff from the mountains. In contrast the Eastern side of the AVA enjoys sun well into the afternoon, resulting in higher daily averages, yet has to deal with denser morning fog, though the permeable gravel and sandy soils offer excellent drainage.

While the conditions on each side of the AVA offer somewhat differing results this remain firmly Cabernet Sauvignon country. Virtually 70% of the area is blanketed with Cab vines, many tended by the most famous names in the business.

The reason for this is of course the quality of the vines those grapes produce. The tannins here are fairly soft but abundant due to the warmth and the wine’s softness is enhanced by the lowish acidity these wines may have. There are rarely problems of immaturity with the fruit here though some notes of herbaciousness and earth are generally noticeable through the dense core of fruit. Other grapes commonly found here are the blending grapes Merlot and Cabernet Franc, with a handful of Chardonnay and Sauvignon Blanc vines still in evidence.

Oakville - Well if any AVA vies with Rutherford for the crown of King of Cabernet it would have to Oakville. Here we find the cradle of the Modern California wine industry. In 1868 a gentleman by the name of H. W. Crabb planted a vineyard, which he named To Kalon, Greek for “most Beautiful”. Saying Crabb was prescient is the under-statement of the year! The To-Kalon vineyard has been responsible for some of the most profound wines ever to emerge from Napa Valley. Long the heart of the famed Mondavi Cabernet Reserve, the vineyard’s fruit is prized to this day.

Slightly cooler than Rutherford, yet warmer than Yountville, Oakville has nearly ideal conditions for viticulture. The soil here is much like that of Rutherford’s with slight differences from east to west though the alluvial deposits tend to be a bit finer here. There are gravely ridges throughout the AVA offering excellent drainage for the Valley floor. The terrain here is more varied than that of Rutherford, with vineyards creeping up the bench lands that shoulder the alluvial flood plains and up into the hillsides that frame the valley.

The results can be a bit confused and in a way the Oakville AVA is one of the least consistent and integral of the valley. Part of this lies in the fact that Cabernet Sauvignon, yet again, dominates the AVA. This fact makes it easy to compare and contrast wines from throughout the AVA, quickly revealing the subtle differences.

Both the valley floor and bench land wines are classic Cabernet with ripe, yet just slightly austere tannins and solid acidity due to the slightly cooler temperatures the region enjoys. The fruit here, while ripe and fruity, is a bit more restrained and elegant than that grown either to the north or at higher elevations. The wines from the hillsides tend to be more powerful and structured and could easily be confused with the mountain AVAs that border these vineyards.

Yountville - To the south of Oakville and comprised virtually entirely of valley floor land, Yountville is the southernmost end of the historic vineyards of Napa Valley. The climate here changes significantly due to the direct maritime influence from the San Pablo Bay as well as the effests of the swampy marsh soils that begin just south of the town of Yountville.

While the soils to the north of town are similar to those of Oakville, though perhaps a bit more compact and finely grained, they are even more diverse and layered with more heavy clays representing centuries of the decay and wash of the upper valley and hillsides.

This is a transitory area where the Cabernet dominant vineyards of the north yield to the Chardonnay and Pinot dominated vineyards of the southern edges of the valley. That is not to say that Cabernet is not grown here but both Merlot and Cabernet Franc may be both more important and distinctive. The style here is round and can be softer than to the north. The effect of the cooler climate being offset somewhat by the richer and damper soils, though the top half of the AVA is known for their age-worthy “cool climate” style.

Stag’s Leap District - Mostly embedded in the eastern edge of the Yountville AVA lays the Stag’s Leap District. This hilly region at the edge of the Vaca range overlooks the valley floor and catches long hours of the suns heat, resulting in some of the hottest average daily temperatures in the Valley. With very dry, rocky soils and a geological position directly in the path of the valley’s evening air outflow, the Stag’s Leap District benefits from quickly cooling evening temperatures. This variance in temperature combined with the unique soil here yield very distinctive wines.

The Stag’s Leap AVA was, in fact, the first AVA to be awarded solely on the basis of unique soils. The distinct attributes these layers of poor volcanic soil intermixed with patches of loam and clay impart to the wines are unmistakable. The wines are clearly the product of a warm meso-climate but the poor soils results in balanced, rich wines with very fine structure perfectly in-tune with the fruit. The wines that spring from these basaltic shelves are unusually malleable and the producers in the Stag’s leap AVA have an unmatched opportunity to craft the style of their wines.

This is red wine country with Cabernet being king but the region is well suited to Zinfandel and Petite Sirah as well as the Bordeaux blending varieties. Merlot can be particularly successful.

Oak Knoll District - The Oak Knoll District represents the southern terminus of Napa’s valley floor vineyards. Extending from the Yountville AVA in the north to the Napa city limits in the south, this low-lying and southerly location produces very cool conditions for the area, conducive to a long growing season and suitable for a wide range of grapes.

As can be expected the soils here are heavy with loam and fine clay sediments. They tend to retain moisture as well as the heat of the day, contributing to the fog the area is famous for, but also warming early in the spring and cooling later in the fall.

The combination of cool climate and fairly rich soils has created the right conditions for Napa Valley's most complex array of grapes. Merlot, surprisingly, is the King and Chardonnay the Queen both made in a ripe yet precise style with a sapid character and fine, delicate fruit notes. Cabernet is fairly abundant though it can seem a bit timid when compared to the gob monsters produced up north. Pinot Noir and even Riesling have found a home in the Oak Knoll District.

Coombsville - Like Calistoga this is an AVA in waiting. Located to the southeast of the Oak Knoll District. Thin and rather small this district combines aspects of the southern regions, the cool maritime influence, with aspects that resemble the Stag's Leap district. The west facing vineyards and poor, basaltic soils Much like the hills of Stag's Leap these eastern hills in the AVA benefit from late afternoon sun and an the unique soil.

This is still red wine country where Cabernet shares the stage with Merlot and Zinfandel. these gently sloping low hills are responsible for some particularly fine Bordeaux blends that benefit from the fairly warm daytime temperatures but the wines maintain a sense of elegance married to power.

Atlas Peak - To the east of both Stag’s leap and the Oak Knoll District lies Atlas Peak, actually a set of broad, high valleys, only taking it’s name from the most prominent peak in the area, Combining the lower temperature of the southern half of Napa valley with elevations reaching over 2500 feet, Atlas peak has some of the coolest temperatures of all of Napa.

The soils here are volcanic in origin and are very porous and retain heat about as poorly as they do water. The prime vineyards are those with western exposures, soaking up the late day sun before the temperatures drop with the onset of nightfall. This diurnal shift provides excellent result for grapes requiring naturally high acid, and of course for whites.

Sangiovese has a relatively long history here, though early efforts were not inspiring. Zinfandel on the other hand has a history of success in the region with the wines made in a relatively restrained style befitting the cool meso-climate, yet with such excellent balance that they have proven to be particularly age-worthy. Slowly Zinfandel has been replaced by Cabernet Sauvignon here and the Cabernet is elegant and richly flavored though the other Bordeaux Varieties are equally successful here and the region as gaining acclaim with the Rhone varieties Syrah as well as the white Marsanne.

Wild Horse Valley - Just as we began, we end with an AVA that straddles two counties, in this case the Wild Horse AVA that juts over the line from Solano County into Napa. With only about 100 acres under vine Wild Horse is an AVA still waiting to discover itself.

Positioned south of Atlas peak and west of Los Carneros, Wild Horse has a meso-climate that combines a cool maritime influence with more annual sunshine than any other Napa Valley AVA.

The future of this cool, sunny region seems destined to be based on “cool climate” grapes such as Chardonnay and Pinot Noir but the lack of easy access to this rugged region has prevented widespread development.

The unique mineral rich soils of the region coupled with its cool climes has produced wines with pronounced acidity, something of an oddity in the region.


Reply by Gregory Dal Piaz, Oct 30, 2008.

There is a great map here

Reply by Philip James, Nov 6, 2008.

Greg - i wish i had the numbers to hand, but I think that California represents about 50% of the AVAs in the whole of the USA.

Reply by VegasOenophile, Oct 1, 2009.

Thanks for this info! Was fascinating to read through, having just been up there exploring. Good knowledge to have!

Reply by WineForNewbies2, Nov 25, 2009.

This is an amazingly good description of the AVAs in Napa Valley. Kudos for a job well done! I will have to link to this from my site since it's such a great resource.

Reply by Gregory Dal Piaz, Nov 26, 2009.

Thanks. Next year I'm hoping we'll be able to make this more interactive.

Reply by napagirl68, Jan 22, 2010.

OMG~! I am so impressed! as a "Napagirl", you did great, really great! THanks for the rundown on the AVAs... nice to see!!! I am truly bowled over to see this all in one place... great, great, great job!! I am currently into Howell mt. cabs.. although i have been a stringent Stags Leap Cab gal. I just ran into a great deal of 1997 Bighorm Coombsville Cab for 5.99 at discount store!!! The vintage tells it all....1997 was a phenomenal year in Napa and CA....

Reply by Cathy Shore, Mar 5, 2010.

A place I have long wanted to visit.  Thanks for the great insight - I'll get there one day.

Reply by Gregory Dal Piaz, Mar 8, 2010.

Sooner rather than later I hope!


Reply by MarkAse, Apr 8, 2010.

I think California is 50% of the AVA's, but something along the lines of 90% of the production.  Granted a big percentage of that is the generic jug wine grown in the warmer valley's of the state, but still crazy to think.

Reply by napagirl68, Apr 9, 2010.

Love Howell mtn.. If I remember correctly, Angwin is (or was) a dry town?  LOL!!!  Kinda ironic...

Reply by yoshiyoshi40541, Apr 9, 2010.

Greg, when you set out a task to inform, you never fail! I've read so many of your posts and 'tastings' articles, and have enjoyed many affordable bottles from your recommendations - so thanks, first of all!

On another note, I was thinking of giving myself a graduation gift and making the trek up to Napa after stopping over to visit friends in San Fran this summer...But as a beginner, I feel so overwhelmed with the number of options I have and need some help narrowing things down. If you had one or two nights to make a quick hop over there, what wineries are on your "absolute, must visit" list? [Keep in mind that my friends and I are lovers of reds, generally jammy or peppery wines]...Any recommendations would help!

Reply by Gregory Dal Piaz, Apr 12, 2010.

Yoshi, let me ask you what you want to take away from a visit.


Are you trying to find the best wines you can, the most individualistic wines, the besty tastings, the best tasting experiences, ie view, people and wine?


Let me know and I'll see what I can do.


Thanks for your kind words, they are very appreciated by the way!

Reply by yoshiyoshi40541, Apr 14, 2010.

Oh my gosh, those all sound like things I'd want to get out of the experience....I guess my top choices would be finding the most individualistic wines, best wines, and best tastings.....Would it be too much trouble to do a run through of each? Maybe two or three vineyards per category...? Haha, I'm such a beginner..Thanks again for all the help! :)

Reply by outthere, Apr 14, 2010.

A nice Rutherford tasting is at Quintessa on the Silverado Trail on the eastern side of the AVA. Was just there last weekend and had a blast. Winery tour, vertical tasting and an opportunity to blend barrel samples to see how blends change the taste of each block. Real educational experience.

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