Local Terroir

Geological Influences

Tectonic shift has been the dominant influence on the geology of San Luis Obispo County, specifically the eastward movement by the Pacific Plate toward the North American plate. This action created mountains through shaving off ancient seafloor, volcanic activity, and uplift along fault lines. The rise of these various mountains and ranges eventually drained inland seas, exposing different types of soils, from limestone, to shale, to volcanic. The most significant and best-known fault in San Luis Obispo County, and in California overall, is the San Andreas.


Mountains/River/other key influences

There are three mountain ranges within San Luis Obispo County: La Panza, Santa Lucia, and Temblor. The Santa Lucia is a long coastal range running roughly parallel to the ocean from Monterey County, near Carmel, to San Luis Obispo’s Cuyama River. It’s a high range, reaching up to 1,785 m (5,857 feet), and never more than 17.7 km (11 miles) from the ocean. The Santa Lucia Range dramatically reduces the Pacific Ocean’s moderating effect on climates east of the mountains.

The Temblor Range is also coastal, but much further inland than the Santa Lucia. It lies along the border between San Luis Obispo and Kern Counties. It is a relatively new range, primarily formed during the pleistocene epoch by tectonic movement and resulting uplift along the San Andreas and other earthquake faults. Once deep underwater, it’s soils are fossil-pocked marine sedimentary.

The La Panza Range, again one of the coastal ranges, runs northeast to southwest. It’s a short range, about 48 km (30 miles) long and topping out at 727 m (2,385 feet). It is northeast of the town of San Luis Obispo and sits between the Santa Lucia and Temblor Ranges.

The largest river in San Luis Obispo County is the Salinas. It runs approximately 281.6 km (175 miles) from its mountain source near the town of Santa Margarita, northeast of San Luis Obispo city, to Monterey Bay. It’s often referred to as “the Upside-Down River,” because its south-to-north flow is unusual in North America. And, oddly, much of the river is invisible, flowing underground. The Salinas is the longest underground river in the United States. 

The Salinas River has the fourth largest watershed in California, its major tributaries being the Nacimiento, San Antonio, Estrella, and Arroyo Seco Rivers. The Salinas River is an absolutely crucial source of water for agricultural and urban areas in both San Luis Obispo and Monterey Counties. There is continual tension between human demand for its water, engineering work, such as the Nacimiento Dam, intended to claim it, and the river’s importance to natural, wetland habitats. So much of its water is diverted, primarily for agriculture, that the northernmost portion of the river ran dry during the last major drought, 2013-2016.

The Santa Maria River is the most important river in San Luis Obispo County outside of the Salinas River watershed. It runs east to west and forms the border between San Luis Obispo and Santa Barbara Counties. In so doing, it meanders through the Santa Maria Valley AVA. Like the Salinas River, the Santa Maria’s impact on grape growing is supplying water for irrigation, rather than any effect on climate.

By far, and as is the case elsewhere in coastal California, the biggest influence on vineyard climates in San Luis Obispo County is the Pacific Ocean. Regions where its wind and fog are unimpeded, such as western Arroyo Grande Valley AVA, experience long, cool growing seasons with daily high temperatures that are moderate. Where mountains or altitude mitigate those factors, the climate is much warmer. Still, its influence is strong enough that all growing regions in the county have Mediterranean climates.

Of these potential influences, the ones which factor heavily on the vines and wines of San Luis Obispo County are the Pacific Ocean, the Santa Lucia Range, and the Salinas River. The Pacific moderates temperatures all year with its mass and cooling winds. The Santa Lucia Range determines how far inland that influence extends and the extent of its impact. The river doesn’t affect climate in winegrowing areas, but it determines whether or not there’s sufficient water for vines to thrive in the zones that receive very low rainfall.


Soil Diversity

There is substantial diversity in the soils of the county. The two primary base materials are marine sedimentary and volcanic. In mountainous areas, those soils can be close to their original form, though eroded or decomposed. On benches and, especially, valley floors, the soils were deposited by alluvial or fluvial action and thus have loamy, sandy, or clay textures. Drainage rate varies accordingly.


Climate

The climate of San Luis Obispo County is Mediterranean, due to the nearby Pacific Ocean. This gives the area long, dry growing seasons. The weather is generally very sunny, though fog in areas closest to the coast can limit UV exposure starting in the late afternoon and again in the early morning. On the Winkler scale, the winegrowing regions vary from Region I to Region IV. The coolest areas are closest to the ocean and the warmest furthest away.

The Santa Lucia Range limits the eastward impact of the cooling influence of the Pacific. However, wind gaps, such as the Templeton Gap in the Paso Robles area, allow ocean breezes to move much further inland. In the southern portion of the county from Arroyo Grande Valley down to Santa Maria Valley, the mountains are much lower or non-existent. There too, the dramatic cooling influence can reach well inland.

In keeping with Mediterranean climates overall, almost all precipitation in the county falls during the winter months. The annual average can vary significantly, based on proximity to the ocean and altitude. For example, York Mountain AVA, which is in the Santa Lucia Range and close to the ocean, gets about 1,143 mm (45 inches) per year. But the easternmost AVAs of Paso Robles receive just 102-204 mm (4-8 inches) of rainfall in typical years.

Despite the general lack of rainfall during the growing season, some vineyards in the county can be dry-farmed. This is particularly true of locations such as the Adelaida District AVA in Paso Robles. Here, the relatively high altitude enjoys 76+ cm (30+ inches) of rain in a year. And many of its vineyards are on limestone, which can retain water from winter and spring rains well enough to keep vines active through the growing season.

Sub-AVA’s

Location/Geography

The 17,353 ha (42,880-acre) AVA lies 19.3 km (12 miles) southeast of the city of San Luis Obispo. The AVA is also directly southeast of the Edna Valley AVA. It includes much of the drainage basin of Arroyo Grande Creek, which runs generally southwest to the ocean from the Santa Lucia Range.


Name Background

Rancho Arroyo Grande was a Spanish land grant in the area, established on existing farmland in 1842.


Topography/Elevation/Water Sources/Geographic Features

The AVA is in a northeast-to-southwest valley which includes hill (Santa Lucia Range) and valley floor terrain. Altitudes range from sea level to 304.8 m (1,000 feet).  


Geology/Soil Composition

Silty clay loams and sandy clay loams with depths and draining ability. Vineyards tend to be on the more shallow, well-drained soils. Origin is predominantly marine, but there are also volcanic influences washed down from the hills.


Climate

Warm-summer Mediterranean, Winkler Regions I and II. Areas closest to the ocean are the coolest and foggiest. Areas in the hills to the east are warmer and sunnier. In general, the AVA is warmer than the Santa Maria Valley AVA, but cooler than the Edna Valley and Paso Robles AVAs.

Average maximum temperatures in the heart of the growing season are in the  low- to mid-30s C (90s F), but days above 37.8° C (100° F) occur every year. A diurnal shift of 16.7° C (30° F)  is common, due to cooling ocean breezes at night. During spring, those breezes are cold enough to delay budbreak, leading to a shorter growing season than some other SLO County regions.

Average annual rainfall is 50.8 cm (20 inches), the vast majority of which falls during winter.


Main Grape Varieties

Chardonnay, Pinot Noir, Rhone varieties, Zinfandel

Location/Geography

Edna Valley is a 9,065 ha (22,400-acre) AVA located directly southeast of Highway 101, with its northern tip extending into the town of San Luis Obispo. It is directly northwest of the Arroyo Grande Valley AVA.

Edna Valley runs northwest to southeast. It is bounded by the Santa Lucia Range on the northeast and the San Luis Range to the southwest.

The western extent of the AVA is just 8 km (5 miles) from the Pacific Ocean.


Name Background

Named for the small community of Edna within the valley, established circa 1883.


Topography/Elevation/Water Sources/Geographic Features

Altitudes are 72.5-146.3 m (238-480 feet). Dry-farming is possible in some areas. Wells provide water as needed.


Geology/Soil Composition

Sandy clay loam, clay loam, and clay, typically with some calcareous material. They’ve historically been free from phylloxera, enabling own-rooted vines.

Primary soil series include Diablo, Los Osos-Diablo Complex, Tierra, Salinas, Cropely, Zaca, and Arnold.


Climate

Warm-summer Mediterranean and mostly Winkler Regions II. A few small zones are Region I.

The climate is moderated by proximity to the Pacific Ocean, so temperatures are less extreme than areas further inland. The combination of warm, sunny days and cooling, marine winds give the Edna Valley AVA a very long growing season, arguably the longest of any California AVA. The breezes and morning fog primarily come from Morro Bay, about 24 km (15 miles) northwest of the AVA, flowing unimpeded through Los Osos Valley on the way.

Average annual rainfall is 50.8 cm (20 inches), the majority of which falls during winter.

Main Grape Varieties

Chardonnay, Pinot Noir, Syrah

Location/Geography

The Santa Maria Valley occupies the northern perimeter of Santa Barbara County on California’s Central Coast. Encompassing 2,696 vineyard acres (1,091 ha), it is bordered on the north by San Luis Obispo County and to the east by Ventura County. Its southern and western boundaries follow the coastline of the Pacific Ocean.


Name Background

Santa Maria was chosen from the name Juan Pacifico Ontiveros had given to his property. Originally named Central City, the name was changed to Santa Maria on February 18, 1885, since mail was often being sent by mistake to Central City in Colorado. Streets named after the four original settlers now form a six-block square centered at Broadway and Main Street, the center of town.


Topography/Elevation/Water Sources/Geographic Features

The Santa Maria Valley boasts a rare “transverse” geography, an east-west orientation that channels cool ocean air directly into the valley. The result is a Mediterranean climate that produces one of California’s longest growing seasons. Grapes in the region are either grown on the Santa Maria Bench or off the Bench, each resulting in grapes with completely different and unique flavor profiles. In 2011, the AVA was expanded by 18,790 acres (7,604 ha) and the addition of nine vineyards. A small section of the appellation lies north of the Santa Maria River in San Luis Obispo County. Elevations range from 200 to 3,200 feet (61 to 975 m), with vineyards planted between 200 and 1,600 feet (61-488 m).


Geology/Soil Composition

With its geological oddity and natural funnel-shape, the Santa Maria Valley AVA is bounded by the San Rafael Mountains and Los Padres National Forest to the east and by the Solomon Hills and the city of Santa Maria to the West. Soils vary by elevation, with sandy loams and silt in the western half of the AVA. Well-draining, gravelly loam and cobbles are found closer to the rivers, along with alluvial and colluvial soils in the Solomon Hills to the south. East of the rivers and moving to higher elevations in the San Rafael Range there are hillside plantings in Chamise clay loam and Chamise shale loam at lower elevations.


Climate

Classified as Winkler I and II, average lows during  the growing season range from the low 50’s to the high 40’s (10°-4°C)and average highs rarely exceed 75°F (23°C). Cooling winds start very early in the day.


Main Grape Varieties

Chardonnay, Pinot Noir and Syrah

Location/Geography

The AVA is a long, narrow, coastal area. It is 408,585 total acres (165,348 ha) in size. It includes within it the Arroyo Grande Valley and Edna Valley AVAs and comprises almost 4,000 acres planted. Just 398 of those planted acres (161 ha), though, are not within the pre-existing AVAs.

The new AVA, in its entirety, ranges from 1.7 to 15.1 miles in width (2.7-24.3 km). 97% of the AVA is below 1,800 feet (548.6 m), which is seen as a significant boundary for the Pacific’s cooling effect. The northern boundary of the AVA is south of the Los Padres National Forest. The eastern boundary is a series of ridgelines in the Santa Lucia Range and also the Los Padres National Forest. The western edge is the Pacific Ocean. The south is essentially Nipomo Mesa.

The AVA, outside of the Arroyo Grande Valley and Edna Valley AVAs,  is distinguished from other AVAs in the county by its extreme, marine-influenced climate and its large concentration of Franciscan Formation, marine sedimentary soils.


Name Background

Both San Luis Obispo Coast and SLO Coast are recognized by the TTB. San Luis Obispo Coast is descriptive, based on the AVA’s location. SLO, pronounced “slow” by those in the know, is an acronym for the county, but also a common and affectionate reference to the relaxed way of life there.


Topography/Elevation/Water Sources/Geographic Features

A coastal region, rising from the ocean to 548.6 m (1,800 feet) in the Santa Lucia Range.


Geology/Soil Composition

Four soil groups:

  • Old Francisican Formation - comprises most of the AVAs soils, especially in the north and central zones. The basis is marine sedimentary (sandstone, shale, and metamorphosed sediments) which have weathered or degraded to varying degrees creating shallow rocky soils, clay loam, and clay, depending on slope and location. Drainage varies accordingly.
  • Loam and sandy loam from young marine and basin sediments. Often requires irrigation. Second most common in the AVA.
  • Volcanic - rare within the AVA and limited to particular areas in the mountains, on the faults, and around volcanic cones. The most dense volcanics can’t sustain vines.
  • Very deep, windblown sand - These soils are found in a very small portion of the AVA. They are generally excessively well-draining and  high in sodium. Thus, they are poor soils for viticulture.

Climate

Warm-summer Mediterranean, Winkler Region I in the areas near the ocean, rising to Region II in Arroyo Grande Valley and Edna Valley, which are more isolated from the ocean by hills and distance.

The petition states that 21% of the proposed SLO Coast AVA has an average maximum growing season temperature of less than 21° C (70 ° F), while another 68% of the proposed AVA has an average maximum growing season temperature of 21-25.5° C (70 - 78° F).

Main Grape Varieties

Chardonnay (43%), Pinot Noir (35%)

Location/Geography

The York Mountain AVA is a 3,885 ha (9,600-acre) area in the Santa Lucia Range, immediately west of the Paso Robles AVA. It is 13 km (8 miles) from the Pacific Ocean. Highway 46 runs east-west through the southern half of the AVA. Its altitude and cool climate distinguish this AVA from the neighboring Paso Robles AVA.

Name Background

The York family long owned property in the area and founded a vineyard and winery in the 1880s. The winery was originally called “Ascension” but was renamed many times in subsequent years (A. York & Sons, York Brothers, York, and York Mountain). The AVA petition was submitted by Max Goldman, then-proprietor of York Mountain Winery.


Topography/Elevation/Water Sources/Geographic Features

This mountainous AVA features altitudes around 457.2 m (1,500 feet). Insufficient groundwater for irrigation. However, high annual rainfall and cool climate enable vines to be dry-farmed.

Geology/Soil Composition

Marine sedimentary soils, primarily limestone and chalk.


Climate

Warm-summer Mediterranean, Winkler Region I.

The area experiences warm, sunny days and cool, foggy evenings due to proximity to the ocean. On account of altitude and ocean proximity, annual rainfall is 114 cm (45 inches) – significantly higher than in other San Luis Obispo County AVAs.


Main Grape Varieties

Red: Grenache, Syrah, Zinfandel and Cabernet Sauvignon

White: Viognier and Roussanne



Location/Geography

The AVA accounts for 247,668 ha (612,000 acres) in northern San Luis Obispo County. In the north, the AVA borders Monterey County. Nested within the Paso Robles AVA are 11 smaller AVAs. Also within the AVA is the town of Paso Robles, which lies almost exactly midway between San Francisco and Los Angeles.

Name Background

Paso Robles is Spanish for “pass'' (or “passage”) of the oaks, a reference to the area’s beautiful oak forests.


Topography/Elevation/Water Sources/Geographic Features

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, flowing down through the center of the appellation, and 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.

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 to 2,000 feet).

Some vineyards on the western side of the AVA are dry-farmed. The rest are irrigated with groundwater from wells or drawn from Lake Nacimiento, a reservoir fed by the Nacimiento River.


Geology/Soil Composition

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. 


Climate

Warm-summer Mediterranean, Winkler regions II-IV


Main Grape Varieties

Cabernet Sauvignon, Syrah, Merlot, and Zinfandel

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 varietals

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

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 cooling Pacific breezes in. 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 (1884-1948), a vice president  of the Southern Pacific Railroad Company.


Topography/Elevation/Water Sources/Geographic Features

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


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 grapes

Location/Geography

Northwest section of the Paso Robles AVA


Name Background

The Mission San Miguel Arcàngel, one of the original 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

Location/Geography

East of San Miguel District


Name Background

The ridgelines come together here like rays of an “estrella,” “star” in Spanish. The local river was also named Estrella


Topography/Elevation/Water Sources/Geographic Features

Rolling plains and terraces 228-554 m (745-1,819 feet) cooled by air flows from 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

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 region (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

Location/Geography

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


Name Background

A synonym in Spanish for “orchard” as the 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

Location/Geography

Inland from Templeton Gap


Name Background

The town of Creston, which was named after 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 near 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

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.

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).

Location/Geography

The southernmost portion 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