Local Terroir

Geological Influences

The Paso Robles AVA, roughly midway between San Francisco and Los Angeles, falls within California's larger maritime- and coastal mountain-defined Central Coast AVA, an appellation comprising the counties of Contra Costa, Santa Clara, San Benito, Monterey, San Luis Obispo, and Santa Barbara.

Four major topographical features define the Paso Robles AVA:

  • The rugged Santa Lucia coastal mountain range to the west, peaking at 631 m (2,070 feet).
  • The Salinas River Valley running down through the middle of the appellation, characterized by rolling hills and small canyons.
  • The Templeton Gap, forged by rivers and creeks running through the Santa Lucia coastal range.
  • The La Panza/Cholame Hills range to the east, rising up to another 609 m (2,000 feet) at the appellation's easternmost edge.

The AVA, which lies entirely in San Luis Obispo County, juts up against the Monterey County line at the north end and is bordered on the south by the Cuesta Grade (the historic road connecting the cities of San Luis Obispo and Paso Robles), just below the small, census-designated community of Santa Margarita. The entire rectangular-shaped region extends approximately 72 km (45 miles) west to east, and 40 km (25 miles) north to south, totaling 247,668 ha ( 612,000 acres). 


Elevation

The City of Paso Robles is approximately 225 m (740 feet) above sea level. Paso Robles AVA plantings east of California Highway 101 generally fall between elevations of 213-365 m (700-1,200 feet). Vineyards on the west side of the highway range from 259-609 m (850-2,000 feet).


Climate and Temperature

As with most California coastal wine regions, the climate of Paso Robles is classified as Mediterranean, characterized by mild winters and warm to hot summers. Rainfall averaging 46 cm (18 inches) is largely confined to the winter months. As of late spring through the summer and into the early fall, until early November, the weather is almost completely dry — ideal conditions for maturation of Vitis vinifera; hence, the 60+ different cultivars commercially grown in Paso Robles.

Where Paso Robles differs from other California wine regions is in its extreme diurnal temperature swings, which are consistently the widest in California. It is not unusual for peak summer days to average 32°-38° C (90°-100° F) and nights to average 7°-10° C (45°-50° F ). Night temperatures close to or below 10° C (50° F)  slow down grape metabolism and acid respiration, which exerts a huge impact on grape chemistry, particularly acidity, freshness and balance in the resulting wines. This also leads to a prolonged growing season and extended hang time.

Therefore, while average growing season temperatures in Paso Robles are slightly higher than in regions such as mid-Napa Valley, the east side of Sonoma County, Bordeaux, and the Northern Rhône Valley, in Paso Robles grapes such as Cabernet Sauvignon and Syrah typically require an extra one to three weeks to reach optimal maturity in terms of Brix and pH balance.

In the experience of Paso Robles growers and vintners, extreme diurnal swings also contribute to increased phenolic content of red wine varieties — particularly the anthocyanins enhancing pigmentation and mouth-feel, and tannins that bolster structure and texture. This unique climatic factor, combined with the AVA's soil chemistry, are why Cabernet Sauvignon now accounts for over half of all grapes planted in Paso Robles. With the use of modern-day techniques to measure phenolics, such as the Adams-Harbertson tannin assay, the phenolic content of both Bordeaux and Rhône varieties grown in Paso Robles is known to be equal to or greater than phenolic content for the same grapes grown in France or elsewhere on the U.S. West Coast.

Climatic and temperature factors defining Paso Robles primarily result from cool marine air that flows east from the Pacific Ocean through the Templeton Gap and south along the Salinas River Valley from the Monterey Bay. Hence, peak summer days are generally warm and cloud-free, maximizing sunlight, with temperature drops at night afforded by a dependable sea fog. There is danger of frost until mid-May, even though April and May average day/night temperature swings average 23°/5° C (74°/41° F) and 26°/7° C (80°/45° F) respectively, and average rainfall shrinks from 3 cm (one inch) to 1.3 cm (0.05 inches) by the end of spring.


Soil

The Paso Robles AVA falls entirely on the Pacific tectonic plate, primarily an ancient seabed. The sedimentary source-rock in this part of the California Coast Ranges is called the Monterey Formation, lifted during the Miocene epoch 17 to 5 million years ago, which has evolved into over 30 parent soil series identified within the Paso Robles AVA. These chiefly consist of bedrock-derived soils from weathered granite, older marine sedimentary rock, volcanic rock and younger marine sedimentary rock. 

Four major soil types exist in the Paso Robles AVA:


Calcareous/Carbonate-rich

Alkaline pHs (7.5-8.2) subsoils

Marine sedimentary

High calcium levels

Low potassium and magnesium levels

Retain moisture in dry months

Good drainage during the wet season


Clay

High pH (7.5+)

Good water retention

Poor drainage

Stays cool, with deep fractures in the dry season

Can also delay ripening, yielding a more acidic wine


Sandy loam

Medium-acidic pH (5-5.8)

Airy soil: tiny particles of weathered rocks typically found on fans, terraces, and with watershed areas

Drains well; poor water retention

Phylloxera-resistant

Often mixed with clay


Siliceous/Silica-rich

Acid-to-neutral pHs (5.5-7.0) subsoils

Medium levels of calcium

Low potassium and magnesium levels

Good heat retention

Good water retention during the growing season

While lower pH clay, sandy and siliceous soil types offer their own advantages, one emerging factor distinguishing the Paso Robles AVA is the high pH content present in many sites. Grapes from these locations are suited to Bordeaux and Rhône red varietals and blends, with a phenolic structure, balanced acidity and aromatic complexity that have become signatures of the appellation, accounting for much of Paso Robles’ recent growth. Paso Robles is also experiencing a resurgence of interest in its heritage Zinfandels, as appreciation for the intrinsic acid balance of Paso Robles Zinfandels and a perceived minerality widely associated with low-pH-style wines has begun to distinguish the region.

Sub-AVAs

Paso Robles’ westernmost AVA is also its most mountainous, with vineyards planted on slopes at 274-670 m (900-2,200 feet) in largely calcareous, patchy colluvium (rocky clay/silt) or Linne-Calodo (shallow loam on shale/sandstone). The climate here is transitional, classified as Region II to III on the Winkler heat summation scale. Heavy alkaline soil types, sometimes called "Adelaida Stone" and distinguished by their propensity to retain grape acidity, also allow for dry farming because of the calcareous layers' ability to hold onto winter rain like a sponge throughout warm to hot growing seasons. Higher elevation hilltop and southerly slopes offer the advantage of increased sunlight in respect to UV intensity -- another reason why the Adelaida District is considered the source of the most structured Bordeaux and Rhône varietals and blends grown in Paso Robles.

Location/Geography

Paso Robles’ westernmost AVA


Name Background

Named for the unincorporated settlement, Adelaida, which lies within the AVA. It has existed since the mid-19th century.


Topography/Elevation/Water Sources/Geographic Features

Mountainous, with vineyards planted on slopes at 274-670 m (900-2,200 feet).


Geology/Soil Composition

Heavy alkaline soil types, sometimes called "Adelaida Stone" and distinguished by their propensity to retain grape acidity.


Climate

Transitional, classified as Region II to III on the Winkler heat summation scale.


Main Grape Varieties

Bordeaux and Rhône varieties.

Due to the influence of coastal air seeping through the Templeton Gap, Paso Robles Willow Creek District is a more consistent Region II than Adelaida District just to the north, with 286-575 m (940-1,900-feet) slopes of largely shallow, calcareous Linne Calodo soils, formed from mountainous, eroded Monterey Formation bedrock. There are also patches of calcareous alluvial loams and clay loams on lower slopes and along stream beds. Limestone, shale and 8.0 soil alkalinity are advantageous in this AVA, supplying proportionate sugar/acid/phenolic content balance to a wide range of varietal wines and blends from grapes such as Syrah, Mourvèdre, Grenache and Grenache Blanc, Viognier and Clairette Blanche, Zinfandel, Carignan, Counoise, Tempranillo, Graciano, Cabernet Sauvignon, Cabernet Franc and Merlot. While higher elevation sites above the fog line see more hours of sunlight, this AVA's high pH soils, combined with moderate temperatures and diurnal swings, help grapes retain acidity while producing some of the most intense and distinctive wines in Paso Robles.

Location/Geography

South of Adelaida District.


Name Background

Named for a creek which runs through the area.


Topography/Elevation/Water Sources/Geographic Features

Slopes at 286-575 m (940-1,900-feet). Higher elevation sites above the fog line see more hours of sunlight.


Geology/Soil Composition

Shallow, calcareous Linne Calodo soils formed from mountainous, eroded Monterey Formation bedrock.  Limestone, shale and 8.0 soil alkalinity supply proportionate sugar/acid/phenolic content.


Climate

Region II on the Winkler heat summation scale, thanks to coastal air seeping through the Templeton Gap.


Main Grape Varieties

Syrah, Mourvèdre, Grenache and Grenache Blanc, Viognier and Clairette Blanche, Zinfandel, Carignan, Counoise, Tempranillo, Graciano, Cabernet Sauvignon, Cabernet Franc and Merlot.

Templeton Gap District, south of Paso Robles Willow Creek District, is defined as a geographic corridor of air flowing from the Pacific, furnishing a Region II to III climate to Santa Lucia Range mountainous slopes and broad alluvial terraces. The AVA's alluvial silt, clay and cobbled loam sites nestle up to rocky calcareous patches at 213-549 m (700-1,800-feet) elevations. While Bordeaux, Rhône and Spanish grape varieties are widely planted, this is where Paso Robles' most established Zinfandel blocks are to be found, producing softer, plumper styles on lower alluvial sites, and higher acid, minerally, more delineated styles on higher calcareous slopes.

Location/Geography

South of Paso Robles Willow Creek District.


Name Background

Named for the area’s defining geographical and climatic feature, a wind gap in the Santa Lucia Range which allows an influx of cooling Pacific breezes. Templeton is a town on Highway 101, and the most prominent town influenced by the gap. The town itself was named for Templeton Crocker, son of Charles Crocker II, VP of the Southern Pacific Railroad Company.


Topography/Elevation/Water Sources/Geographic Features

Corridor of air flows from the Pacific to the Santa Lucia Range slopes at 213-549 m (700-1,800-feet) elevations.


Geology/Soil Composition

Broad alluvial terraces of alluvial silt, clay and cobbled loam.


Climate

Region II to III on the Winkler heat summation scale.


Main Grape Varieties

Paso Robles' most established Zinfandel blocks, along with Bordeaux, Rhône and Spanish grape varieties.

In the northwest section of the Paso Robles AVA, around the little community of San Miguel, San Miguel District typifies warmer sections of the AVA with its Region III-IV climate, yet still marked by 1.6°-4.4° C (35°-40° F) diurnal swings, typical of much of Paso Robles. The AVA's 177-488 m (580-1,600-feet) elevations consist of fairly deep, alluvial sandy loams and clay loams on terraces close to the Salinas and Estrella rivers, with shallower clay hardpans at lower river bottom sites. Zinfandel thrives in this warmer climate AVA, as do Italian grapes such as Sangiovese, Aglianico and Nebbiolo.

Location/Geography

Section of the Paso Robles AVA.


Name Background

The Mission San Miguel Arcàngel, one of the original Colonial Spanish Missions.


Topography/Elevation/Water Sources/Geographic Features

177-488 m (580-1,600-feet) elevations on terraces close to the Salinas and Estrella rivers.


Geology/Soil Composition

Fairly deep, alluvial sandy loams and clay loams, with shallower clay hardpans at lower river bottom sites.


Climate

Region III-IV climate on the Winkler heat summation scale.


Main Grape Varieties

Zinfandel, Sangiovese, Aglianico and Nebbiolo.

While located east of San Miguel District, average growing season temperatures in this largely Region III AVA defined by the Estrella River Basin are influenced by a slightly cooler maritime influence, with air flowing from both the Templeton Gap and the Salinas Valley to the north. Rolling plains and terraces between 228-554 m (745-1,819 feet) are primarily alluvial/sandy loams, with rocky veins of alkaline calcareous base surfacing in shallow topsoils at higher elevations. Diurnal swings of as much as 1.6°-4.4°C (35°-40°F) during the growing season contribute to phenolic structure and acid balance in reds, accounting for the aggressive investment in black-skinned grapes such as Cabernet Sauvignon, Petit Verdot, Merlot and Syrah in this AVA.

Location/Geography

East of San Miguel District.


Name Background

The ridgelines come together here like rays of an “estrella,” (i.e. “star” in Spanish). The local river is also named Estrella.


Topography/Elevation/Water Sources/Geographic Features

Rolling plains and terraces between 228-554 m (745-1,819 feet) are cooled by air flows from both the Templeton Gap and the Salinas Valley to the north.


Geology/Soil Composition

Alluvial/sandy loams, with rocky veins of alkaline calcareous base surfacing in shallow topsoils at higher elevations.


Climate

Largely Region III on the Winkler heat summation scale


Main Grape Varieties

Cabernet Sauvignon, Petit Verdot, Merlot and Syrah

Just south of California Hwy. 46 from Paso Robles Estrella District, Paso Robles Geneseo District is a lower-lying region, 225-396-m (740-1,300-feet) elevation, largely defined by the Huer Huero Creek Watershed. Multiple soil types are marked by gravelly/silty/clay alluvial terraces with some alkaline calcareous elements, sitting on hardpans of gravelly Paso Robles Formation and older granite base rock. Although the climate falls on the warm side of Region III and IV, Cabernet Sauvignon here can retain deep color, pungent spice, some perceived minerality, bright acidity, viscosity, and firm, black tea-like phenolics — including some of the best examples of this variety in Paso Robles.

Location/Geography

South of California Hwy. 46 from Paso Robles Estrella District.


Name Background

The German settlers arrived in the region from Geneseo, Illinois, during the 1880s.


Topography/Elevation/Water Sources/Geographic Features

Lower-lying 225-396-m (740-1,300-feet) elevation), largely defined by the Huer Huero Creek Watershed


Geology/Soil Composition

Gravelly/silty/clay alluvial terraces with some alkaline calcareous elements, sitting on hardpans of gravelly Paso Robles Formation and older granite base rock.


Climate

Warm side of Region III and IV  on the Winkler heat summation scale.


Main Grape Varieties

Cabernet Sauvignon.

Sandwiched between the south end of Paso Robles Geneseo District and the eastern edge of Templeton Gap District, El Pomar District has emerged as a major source of red Bordeaux varieties, particularly softer tannin grapes such as Merlot and Cabernet Franc, which seem to retain deep color, bright fruit and acidity in El Pomar District’s rolling hillsides (225-488 m/740-1,600-feet). Recent plantings of earlier ripening Cabernet Sauvignon clones are also showing great promise. Alluvial soils vary between clay loams and some calcareous sub-soils of Monterey Formation sandstone and siltstone. Proximity to a consistent flow of cool air through the Templeton Gap gives this AVA a Region II climate, veering into Region III. This enables Bordeaux grapes to ripen with minimal pyrazine, while facilitating lush, balanced fruit qualities.

Location/Geography

Sandwiched between the south end of Paso Robles Geneseo District and the eastern edge of Templeton Gap District.

Name Background

Spanish for “orchard.” This area was long known for its almond orchards.


Topography/Elevation/Water Sources/Geographic Features

Rolling hillsides (225-488 m /740-1,600-feet) close to Templeton Gap.


Geology/Soil Composition

Alluvial soils vary between clay loams and some calcareous sub-soils of Monterey Formation sandstone and siltstone.


Climate

Region II on the Winkler heat summation scale.


Main Grape Varieties

Red Bordeaux varieties, particularly softer tannin grapes such as Merlot and Cabernet Franc.

Though further east from Templeton Gap, Creston District rises up from 305 m (1,000-feet) slopes to a 610 m (2,000-feet) plateau towards the base of the La Panza Range. Vineyards are planted on gentle hillsides and terraces, much of it Nacimiento soil series, consisting of well-drained, fine sandy or clay loams layered with calcareous shale, limestone granitic and sedimentary rocks. The climate is classified as Region III, although individual sites at higher elevations influenced by the Templeton Gap fall into Region II in some vintages. Red Bordeaux grapes in particular retain plenty of anthocyanin, tannins, balancing acidity and fruit concentration in this terroir.

Location/Geography

Inland from Templeton Gap.


Name Background

The town of Creston, named for one of its founders, C.J. Cressy.


Topography/Elevation/Water Sources/Geographic Features

Gentle hillsides and terraces on a 305-610 m (1,000-2,000-feet) plateau at the base of the La Panza Range.


Geology/Soil Composition

Nacimiento soil series, consisting of well-drained, fine sandy or clay loams layered with calcareous shale, limestone granitic and sedimentary rocks.


Climate

Region III on the Winkler heat summation scale, although individual sites at higher elevations, influenced by the Templeton Gap, fall into Region II in some vintages.


Main Grape Varieties

Red Bordeaux.

At the far northwest corner of Paso Robles, in the vicinity of the little town of Shandon, San Juan Creek is a warmer Region III to IV climate AVA, averaging some of the widest diurnal swings (-1.1°-10° C/ 30°-50°F) in Paso Robles. Defined by the river valley topography of San Juan Creek, a tributary of the Estrella River, deep benchland alluvial soils consist of sandy loams, clay loams, shale and sandstone, sitting at elevations between 299-488 m (980-1,600 feet). Plantings are dominated by the most popular black-skinned grapes such as Cabernet Sauvignon, Zinfandel, and Petite Sirah.

Location/Geography

Northwest corner of Paso Robles, in the vicinity of the little town of Shandon.


Name Background

San Juan Creek is within the AVA and feeds into the Estrella River.


Topography/Elevation/Water Sources/Geographic Features

River valley topography of San Juan Creek, a tributary of the Estrella River, at elevations of 299-488 m (980-1,600 feet).


Geology/Soil Composition

Deep benchland alluvial soils consist of sandy loams, clay loams, shale and sandstone.


Climate

A warmer Region III to IV on the Winkler heat summation scale.


Main Grape Varieties

Cabernet Sauvignon, Zinfandel, and Petite Sirah.

In the easternmost section of Paso Robles, Paso Robles Highlands District is a warmer climate AVA (Region IV), climbing to heights between 353-636 m (1,160-2,086 feet) and typically experiencing growing season diurnal swings as much as 10° C (50° F). Soils at the base of the La Panza Range are derived from Simmler, Monterey and Paso Robles Formations, and are a mix of older leached alkaline alluvial soils with younger sandy soils along active streams.

Location/Geography

Easternmost section of Paso Robles at the base of the La Panza Range.


Name Background

Paso Robles is Spanish for “Pass of the Oaks.” It’s called “highlands” due to altitude, being in the foothills of the La Panza and Diablo ranges.


Topography/Elevation/Water Sources/Geographic Features

353-636 m (1,160-2,086 feet).


Geology/Soil Composition

Simmler, Monterey and Paso Robles Formations, a mix of older leached alkaline alluvial soils with younger sandy soils along active streams.


Climate

Region IV on the Winkler heat summation scale, with growing season diurnal swings as much as 10° C (50° F).


Main Grape Varieties

Petite Sirah, Cabernet Sauvignon, Zinfandel

In its own corner at the bottom the Paso Robles AVA, well south of the municipal zones of the City of Atascadero, Santa Margarita Ranch shares the characteristic of highly calcareous soil types with the rest of Paso Robles, and its Region II climate is consistently the coolest in Paso Robles. Temperatures are influenced by maritime air funneled in from both Morro Bay and Templeton Gap. While not quite as climatically “cold” as the more southerly appellations of San Luis Obispo County (i.e., the Edna Valley and Arroyo Grande Valley AVAs), grapes like Pinot Noir, Cabernet Sauvignon, Sauvignon Blanc, Chardonnay and Zinfandel can be planted in adjacent blocks, all generating leaner, lighter, acid-driven iterations of their respective varietal profiles — closer, in that sense, to wines of the San Luis Obispo AVA than to wines from the rest of Paso Robles.

Santa Margarita Ranch AVA is essentially a monopole belonging to three families farming Margarita Vineyard, producing wines under the Ancient Peaks Winery label. The area’s 8 km (five-mile-long), 403 ha (996 acres) of vines were originally planted by the Robert Mondavi Winery in 1999 and later reclaimed by the three property owners in 2005. This AVA boasts a phenomenal mix of soils, from ancient seabed, replete with chalky white, fossilized sea shells, and sedimentary shale, to rocky granitic and alluvial clay, embedded in 274-427 m (900-1,400-foot) slopes. Consequently, wines vary according to specific sites, from grippy yet pungent, moderately weighted Cabernet Sauvignons grown in shale and alluvial clay blocks, to higher acid, flowery-scented Cabernet Sauvignons grown in the chalky calcareous blocks.

Location/Geography

The bottom of the Paso Robles AVA.


Name Background

The name of the Spanish mission.


Topography/Elevation/Water Sources/Geographic Features

Maritime air funneled in from both Morro Bay and Templeton Gap


Geology/Soil Composition

Highly calcareous. A phenomenal mix of soils, from ancient seabed, replete with chalky white, fossilized sea shells, and sedimentary shale, to rocky granitic and alluvial clay.


Climate

Region II on the Winkler heat summation scale, consistently the coolest in Paso Robles.


Main Grape Varieties

Mostly Cabernet Sauvignon, with some Pinot Noir, Sauvignon Blanc, Chardonnay and Zinfandel.