, , , , , , , , , , , , , , , , , , , , , , ,

Those who follow me on Twitter have likely heard this already, but I wrote an article on the Geologic history of the Willcox AVA for the latest issue of AZ Wine Lifestyle magazine.  For those interested in the topic but don’t have access to the magazine, I thought I’d repost it in my blog out of the kindness of my own heart:


Still to this day, one of my favorite photos of a vineyard near Willcox.

As a native Arizonan, it is my opinion that the geology of Arizona is one of the major factors which makes our wines so unique and flavorful. This uniqueness allows them to stand against wines from any major region of the world. Currently, Arizona is celebrating the official proclamation of Willcox as our state’s newest American Viticultural Area (AVA for short), and with 74% of Arizona’s grapes coming from this region, it has been a long time coming. Through the tireless efforts of many people for the last 30 years, from the late Al Buhl who was among the first to grow in the Kansas Settlement, to John McLaughlin, who helped fund the AVA application process to the TTB, along with the Arizona Vigneron’s Association and their efforts to bring Arizona wine into the mainstream, this long process has finally come to a successful harvest. It is now our turn to rejoice in the work of the growers and vintners whom have cultivated and bottled this land for us. The landscape here has a storied history of tireless workers, and I raise a toast to all of them. But, for me, I’m as interested in understanding the landscape of Willcox in its geological context in relation to terroir, as I am of understanding the palate of the wines produced there. The landscape here has a long and fascinating story.

The story of Willcox wines truly begins in the Precambrian Epoch, almost one and a half billion years ago. The granite and metamorphic rocks that form the basement rock of Arizona, and emerge from the desert to form the mountains that make the dramatic backdrop for the Willcox AVA. These rocks show evidence of violence—of a continent slowly coalescing into shape from volcanic island arcs and cratons. Coronado Vineyards, located at the old Willcox Country Club, grows their vines in soils eroded from these Precambrian deposits. These rocks did not originally form as mountains; instead, they often formed deep underground, and were long buried.


The mountains behind Coronado Vineyard, along with the vineyard itself, are on Precambrian granites.

These rocks were buried by the ebb and flow of the ancient seas that once covered this land during the era which geologists refer to as the Paleozoic. The majority of their layers are known as the Martin Formation and the Naco formation. These layers of limestone and dolomite are roughly the same age as the red rocks of Sedona, though here, the sea was much deeper as the area was the heart of the lost, tropical Pedregosa sea. Fossils left behind show an average depth of around 150 feet, and, as a fun side note, rocks near the town of Dos Cabezas at the edge of the Sulphur Springs Valley are the type locality for several species of ancient sharks. It was the rise and fall of these ancient seas which formed the underlying rock that secured the aquifer which supplies Willcox’s signature vines; those vines which have made Willcox famous.

There is a gap in the rock record in this landscape, following the departure of the Paleozoic seas. Rocks in nearby Sonoita help fill some of that gap, telling a story of volcanic eruptions forming mountains like the Andes, punctuated by desert sands and dinosaurs. The story returns in detail during the Early Cretaceous period, when some of these Andes-style volcanic mountains began to erode by the shores of the sea, which returned to grace the presence of our land one last time before disappearing for good. This time, though, the waters were an extended arm of the Gulf of Mexico. Other mountains which once existed here were rocked by explosive volcanic eruptions which left thick deposits of rhyolite and andesite. In other places, granite intruded into the landscape. The iconic two-headed profile of the Dos Cabezas mountains which loom over the valley is the most recognizable example of such activity preserved in the current landscape. These ancient mountain ranges were known as the Mogollon highlands.


The Dos Cabezas preserve a hint of the Mogollon Highlands in their two heads.

Volcanism was, as it turns out, the general rule of thumb in this region up until about 16 million years ago. Later into this period of the Cenozoic, massive super-volcanic eruptions left layers of welded tuff that are many hundreds of feet thick in places. These deposits form much of the land in the Chiricahua foothills, where Aridus, LDV, and Keeling-Schafer grow their vines. Most of the rocks from this period aren’t in the AVA, except in the region near Pierce and Dragoon. The unique terroir of the area around these portions of the Willcox Basin owes itself to the same unique geology that made this part of the region a hotbed for mining activity. A massive influx of mineral-rich porphyritic granites that intruded during the same period that the Chiricahuas were exploding provides a unique suite of spice flavors different from that present in the wineries of the Willcox Bench. These characteristics are prominently manifested in wines from Golden Rule Vineyards (and which I predict will also manifest in the estate vintages from Four-Tails).

The next stage of the geological history of the Willcox AVA was no less violent. This period was one that brought dramatic changes to the landscape during the late Tertiary, as dramatic crustal stretching occurred, creating what is known to geologists as the Basin and Range Province. The old Mogollon Highlands of the Cretaceous and early Tertiary collapsed, and new mountains emerged from their remains as crustal extension, reactivating long-dormant Precambrian faults which had been buried for billions of years. The immense pressures associated with mountain-building and the activation of these faults compacted and folded existing strata into sinuous anticlines and synclines. In some places, these strata were almost warped atop themselves as they were thrust upwards into the sky from deep within the earth, creating the sky islands (such as the Dragoon, Chiricahua, and Mule Mountains) that surround the valley today. These mountains, as they eroded, slowly filled the valley with debris. The Sulphur Springs Valley became completely isolated from outside drainage, which set the stage for the most integral part of the Willcox AVA: the Willcox Bench.

The enclosed nature of this basin, which offers no outlet for water to drain from, allowed for large quantities of water to be retained within the valley during the cool, wet periods during the ice age that occurred between roughly 2 million and 12,000 years ago. This created a lake, known as Lake Cochise, which waxed and waned with the climate, disappearing eventually. At its greatest extent, the lake was likely about 35 feet deep, and 75 square miles. The lake left behind fertile shores and beach ridges at this extent, where soils and rock that had eroded from the mountain were mixed together by wave action from wind and water. It is one of these ancient beach ridges that forms the present Willcox Bench. Here, near Robb’s Road, is where a myriad of wineries grow: Carlson Creek, Flying Leap, Pillsbury, Sand-Reckoner, Zarpara, Rolling View, and Caduceus all have vineyards on the Bench. This area of slightly richer soil is at a slightly higher elevation than the rest of the Kansas Settlement, making it fantastic for grape growing Red wines made from grapes grown on the Bench always smell to me like the dust from the dirt roads that criss-cross this area; whites seem to pick up the minerality and limestone from the caliche layers left behind by the lake, and possess intense floral notes as well.

2014-05-22 15.32.56

Tempranillo Vines in Willcox

For the geologically-minded wine drinker, terroir is the signpost of history. The geologist, with their training and sharp eyes, can see landscapes that are long gone, present only in fragments. The drinker of wine who knows the deepest history of a place can take that fragment and taste it. You can parse the wine in your glass like a dead language, and make it alive by saying, “This wine smells of the ancient sea crashing upon wild shores,” and mean every word. I feel that an understanding of the geological history of a place enhances the enjoyment of a wine from that region. Terroir not only tells you where the grape is from today; through the lens of geology, it tells you where the grapes were from in the deepest of yesterdays. It is those yesterdays which make the wines of Willcox so intriguing. And now that you, dear reader, know the geological history of the present Willcox AVA, you can enjoy those wines all the more.