Paso Robles Terroir

Paso Robles, only 30 miles (50 km) long and 40 miles (65 km) wide, contains most of the world’s climates that are suitable for grapes. It’s possible to grow the cool climate loving Sauvignon Blanc next to the sun-seeking Zinfandel in the same small region. Let’s find out why!

Situated between Los Angeles and San Francisco, sitting at the same latitude as Crete and Tunisia (35°N), you’d expect this area to be really warm and dry, and you’d be right! In some parts of Paso Robles we find grapes that love the heat, like Zinfandel and Petite Sirah. But there are also cooler pockets where Pinot Noir and Sauvignon Blanc thrive too!

Let’s find out the aspects of Terroir in Paso Robles that allow this small AVA to produce over 60 different grape varieties!

There are three main factors that contribute to Paso Robles’ terroir:

  • Wind and Fog
  • Diurnal Range
  • Unique Soils
Gaps in the mountains bring wind and fog

Wind and fog cool things down, making these areas perfect for Pinot Noir and refreshing styles of Cabernet Sauvignon.

Paso Robles, though only 20 miles (30 km) from the cold Pacific Ocean, is separated from it by the Santa Lucia mountains. With an elevation of over 1600 ft (500 m), these mountains prevent most of the cool Pacific breezes and fog from reaching Paso Robles.

However, in key areas, there are breaks in the range, which allow for wind and fog to slip through, cooling areas within Paso Robles. The two main gaps are:

  • The Templeton Gap
  • The Cuesta Grade

Early morning fogs at Bon Niche Cellars in the Estrella District of Paso Robles.

The Templeton Gap, located just east of Paso Robles, allows fog and wind from Morro Bay to get through the mountains. This cools off the AVAs of York Mountain, Adelaida District, Willow Creek District, El Pomar District, and the Templeton Gap District.

These AVAs have climates that are similar to Bordeaux. This is perfect for growing Cabernet Sauvignon, but also cool enough to grow Pinot Noir and other varieties that prefer cool areas.

The Cuesta Grade funnels cool air and fog from Pismo Beach, bringing cool air to the Santa Margarita Ranch AVA - another great place for Pinot Noir. The further away from these gaps, the warmer it is and the more heat loving grape varieties we find.

Cold night air cools things down and brings freshness in the wines

Diurnal range is the temperature difference between night and day, and Paso Robles has some pretty crazy numbers - you can see a 50°F (30°C) change between night and day here!

Massive swings between day and night temperatures mean that even if it’s as hot as 100°F (38°) during the day in August, the temperature can plummet at night to 50°F (10°C).

This means the vines are able to refresh themselves, the grapes hold on to their acidity, and the aromas are retained in the berries. The result is that you get ripe fruit flavors and tannins, but lots of refreshing acidity and aroma too.

Why does Paso Robles have one of the highest diurnal swings in California? There are lots of places where cold air sneaks in during the night:

  • Monterey Bay to the north
  • Downslope winds from the Cholame Hills to the east
  • Pacific winds from the west

These combine to create some pretty chilled out evenings - so bring your sweater if you’re visiting!

This diurnal swing is intensified by altitude and distance from the ocean, therefore higher vineyards see even bigger swings as do vineyards further away from the Pacific, such as wineries in the Estrella District, San Juan Creek, and the Highlands District.

Tectonic Plates and Unique Calcareous Soils

Paso Robles has unique soil characteristics that are not easily found in other parts of North America because Paso Robles sits on a completely different tectonic plate than the rest of the continent. This leads to a freshness in the wines.

The Pacific tectonic plate, where we find Paso, meets the North American plate at the San Andreas Fault. The pushing and sliding of these plates over millennia has resulted in unique soils: a whole lot of ancient seabed, full of fossilized sea creatures, and their skeletons full of calcium carbonate.

These calcareous soils give the wines freshness and acidity. Another amazing thing about calcareous soils is that they hold water really well. This means in areas that get enough rainfall, 25-35 inches (650-900mm) per year, dry farming is possible.

In addition to the limestone and calcareous soils that are unique to Paso Robles, there’s also a diverse viticultural playground thanks to the diverse soils.

This means it’s possible to find the perfect terroir for many different grapes.

Rich limestone (calcareous soils) is all over Paso Robles like these at Caelestra Vineyard in Templeton Gap.

Calcareous soils: Create fresh wines with lots of acidity. Make for deeply colored Cabernet Sauvignon with angular tannins. These soils are pale in color and are made up of ancient seabeds that are pushed to the surface by tectonic plate movement.

Sandy Loam: Gives a fruity side to wines. Petite Sirah loves it, but so does Cabernet Franc. Sandy Loam is a bit of a mix of everything; decomposed calcareous soils with clay and sand, some old granite, smaller bits of larger rocks too. It doesn’t retain water well so vines need irrigation, but it makes for really fruit-driven wines.

Siliceous soils: This means full of Silica, and are therefore very sandy soils. Grapes grown on these soils make light, very aromatic wines. There’s some lovely, elegant Pinot Noir grown on Siliceous soils in Paso Robles.

Clay: Clay soils hold water really well and are cooler in temperature. This means grapes are able to hold on to acidity a bit longer, and therefore wines can be fresh when grown on clay. Cabernet Sauvignon grown on clay tends to be fresh but also have an opulent and smooth side to it.


♦ Paso Robles: An American Terroir, Thomas J. Rice, Tracy G. Cervellone, 2007

Paso Robles Wine Country Alliance