A SE-NW transect across the Eden Valley and the Barossa Valley (Barossa Grape and Vine, Caro Graphics). The distance between Springton and Greenock is 32-33 kilometres. Naturally the altitude has been greatly exaggerated. This transect direction is unusual but I did not have time to do one myself.
The Landscape Setting of the Eden Valley
The Eden Valley is a very picturesque wine region noted of course for excellent riesling and very interesting shiraz flavours, the latter much loved I recall be the great Penfolds winemaking genius Max Schubert. This short article is to give you a better understanding of the landscape, how it was formed and some of the features that will affect the taste of the wine.
Eden Valley is a hilly plateau and valley that adjoins the Barossa Valley to the east and is roughly 200 metres higher than the floor of the Barossa Valley. The highest peaks, which are called the Barossa Range, can be 300 metres higher. The most famous of these peaks are Kaiser Stuhl, at 580 metres and Little Kaiser Stuhl at 560 metres. Directly west from these peaks the landscape falls quickly into the Barossa Valley and at Rowland Flat, the site of the production facility of Orlando, the elevation is 220 to 240 metres.
I won’t dwell on the geology but the Eden Valley, the Barossa Valley, the Adelaide Hills and many other vineyard locations are small enclaves in a vast sweep of rocks which run from Kangaroo Island, along the Fleurieu Peninsula and into the Flinders Ranges before disappearing under the desert sands.
For the area that interests us, from McLaren Vale to the Clare Valley these rocks create a roughly north-south running set of ridges and valleys. The valley streams can run either north or south before breaking out westward to the ocean.
The Eden Valley is in simple terms an elevated eastern ridge, a valley and a western ridge (the Kaiser Stuhl side). Flowing north down the valley is the North Para River which finally turns near the town of Angaston, in a magnificent arc, break through the western ridge line and flows south down the Barossa Valley.
A few million years ago it is likely that the Eden Valley was a low range of hills perhaps only 50 metres higher than the floor of the Barossa. Much earlier, going back 35-50 million years ago, today's ridges and valleys were all part of a flat, deeply weathered, rolling peneplain. Remnants of this old surface can be found in the Eden Valley.
A fault line called the Stockwell fault separates the Barossa and Eden Valleys and this fracture is dated as beginning about 35 million years ago.
This fault line lifted the Eden Valley side of the landscape, perhaps in a series of steps. This had an important consequence. Prior to this disruption there had been a long period of stability and as suggested the landscape was probably a rolling flat land or peneplain complete with a hard ironstone cap. This surface protected a deeply weathered profile tens of metres in thickness which had formed naturally between the fresh basement rock and the surface. This ‘weathered zone’ undergoes interesting chemical changes as the fresh rock is altered. It replaces the surface soil as it is eroded.
What happened during the time between the first upheaval 35 million years ago and the more recent upheaval, perhaps commencing two million years ago, is a matter of conjecture. In the Barossa region there is a distinctive rusty-red coloured rock I call Barossa Ironstone. I believe this was formed during a hot, dry period. I use it as a marker horizon though whether it is all of the same age is difficult to prove. I guess the age of this horizon at 10 million years. Remnants of this horizon are seen in the Eden Valley hills at Gravel Pit road (510 metres), the very end of Rocky Valley on Menglers road, and along Tanunda Creek road. If this 'Barossa Ironstone' is the same as that in the Barossa Valley it signifies an uplift of 210 metres, based on the nearest Barossa Ironstone in the Valley near Stockwell which is at 300 metres.
This recent upheaval then has lifted the surface of Eden Valley some 200 metres above the Barossa Valley and the low hills which bound the west of the Barossa Valley. This disrupted what remained of the old 'peneplain surface' and led to the rapid and almost complete erosion of all of the weathered rock lying below this hard cap. This uplift, which would not have happened in one movement, allowed erosion to proceed faster than fresh rock could decompose and create new soil.
The Vineyards Today
In summary not only were the previous soils eroded but almost all of the great thickness of decomposed rock has also eroded. A striking landscape feature of the Eden Valley is the creation of ‘tombstones’ which are slabs of fresh rock that stand up above the soil level and are often found in rows. These rows express the geological grain of the country.
A few years ago I followed a soil expert working along Flaxmans Valley road. A number of vineyard owners had joined together to get an assessment of their vineyards allowing the hiring of a drilling rig which moved from property to property and ended up at the Yalumba owned vineyards of Pewsey Vale and Heggies. My overriding impression was the thinness of the soil with cores being as short as 10-20 centimetres before grinding into fresh rock. In a few there was no effective soil at all. A thin, sandy, black top soil was often followed by a grey, sandy, sub-soil often stained with iron. Most of this is wind-blown and is very recent meaning not much in the way of soil has been contributed by the underlying rotten rock.
So the Eden Valley of today is a landscape of thin and very poor soils often only inches deep which barely cloak the fresh rock. In many areas it is cloaked with recent wind-blown sands. The zone of weathered rock which customarily sits below a soil has minimal thickness or does not exist. Much of the soil that exists is made from windblown sands and silt which has been trapped by the vegetation.
Thus the Eden Valley differs from the Barossa Valley not only from the elevation which creates a wetter and cooler climate but also from very thin soils, most noticeably on the peaks and slopes. Only on the lower slopes close to the river do you get deeper soils which of course have formed from the accumulation of particles washed down from the higher peaks.
Not only are the soils impoverished but they do not retain moisture two factors which inhibit vine growth and crop levels. Exactly what impact this has on wine quality is not fully understood.
* Please note the comments about soils are generalisations. Eden Valley is a very large region and all I have seen are selective snap-shots, most from along the western side.