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Santa Margarita District

June 9, 2021

The Santa Margarita Ranch American Viticultural Area (AVA) is quite possibly the most unique of all the 11 Paso Robles districts. It is at the southern boundary of the over 600,000-acre area that is the Paso Robles AVA, nestled up against the Santa Lucia Mountain Range. It stands alone, meaning that its boundaries do not border any of the other Paso Robles districts. The headwaters of the Salinas River, which helps to define the greater Paso Robles AVA, begin in the surrounding mountains and feed the river from the spillway of Santa Margarita Lake. As the river runs to its northern mouth on Monterey Bay, its origins trace the northeast boundary of the Santa Margarita AVA. Historically this region was seen as a lush environment, perfect for farming a multitude of crops and perfect for grazing land.

A Brief History

The naming of the Santa Margarita area originates from the original Mexican land grant in the mid-1800s and after the unique mission that existed there, the Santa Margarita de Cortona Asistencia. Asistencia, or “assistant mission”, served as the most northern outpost of Mission San Luis Obispo de Tolosa, which is the mission of the nearby town San Luis Obispo. The outpost is sometimes referred to as San Luis Obispo County’s “third mission.” A cement/stone building was erected in the valley northeast of the Santa Lucia Range and dedicated to its patroness, Santa Margarita. The building still stands, and the current day owners of the property have built a large barn over the remaining structure to help preserve it. It is written that the original structures were used to house grain, served as a chapel, and had living quarters as well.

At the time that the Asistencia was built, grapevines were planted on the ranch by the Franciscan friars. Much like the rest of California during the establishment of the mission system, farming and the raising of livestock was introduced which signaled a major shift on how the native culture and their system of living off the land was changed into an agrarian society.

In the years following, Santa Margarita would become a Wells Fargo Stagecoach stop as well as a train stop for the Southern Pacific Railroad. This southern extension of the Southern Pacific from Templeton was the impetus of a new planned community on a 640-acre townsite adjacent to the railroad in1889. Instrumental in this development was the landowner Patrick Murphy who came to own the Santa Margarita rancho following the United States’ annexing of Alta California.

Viticultural Beginnings

The first grapes were planted 200 years ago by the missionaries and since that time viticulture had not played a role in the region’s agricultural development until Robert Mondavi Winery leased over a thousand acres for vineyard development in the 2000s. Many years of planting and development ensued after, as well as a change in ownership. The vineyard originally developed by Mondavi Winery is now over 850 acres with 16 varieties of wine grapes. The Santa Margarita Ranch viticultural area encompasses an area of approximately 18,300 acres.

Setting and Climate

The Santa Margarita Ranch viticultural area is situated along a valley floor populated by many Oak and Sycamore trees. The watershed is characterized by the Salinas River and its tributaries including Santa Margarita Creek, Yerba Buena Creek, Trout Creek, Burrito Creek, and Rinconada Creek. Elevations in the Santa Margarita area range from 900–1,400 feet above sea level. The Salinas River, which borders the northern boundary, abruptly changes its course moving from the wider valley floor it excavated earlier into a canyon it cut more recently through the soft Monterey formation.

A distinctive maritime and mountain-valley climate exists in the Santa Margarita Ranch, which is different than the other viticultural areas within the greater Paso Robles AVA. Regions to the north, like the Templeton Gap and Paso Robles Willow Creek districts, have lower daytime highs and slightly higher nighttime lows due to the marine influence of the Templeton Gap effect. The narrow valley of the Santa Margarita Ranch is surrounded by mountains on three sides so the maritime influence is less, along with the accentuated orographic influences that bring more rainfall, approximately 29 inches in an average year. This also means higher daytime high temps and lower nighttime low temperatures. This is a direct reflection of the topographic influences and mountain/valley breezes.

Geology and Soil

The Santa Margarita Ranch viticultural area is nestled up against the Santa Lucia Range and well reflects the marine sedimentary material that is all over the Paso Robles region. However, Santa Margarita also has granitic rock due to faulting and movement along the San Andreas fault zone over that last few million years which accompanied the uplift of the Santa Lucia Range. The valley floor of the Santa Margarita area was originally formed by erosion from the Salinas River, the river at some point in the last few million years carved a channel through the soft Monterey Formation shales along the Rinconada Fault, as the San Andreas Fault zone became more active. This created a broad alluvial fan and terrace deposits across the area, these terraces are largely at the 1,150-1,350 ft elevation. The viticultural landscape also sees deep gravelly loam soils as well as shallower clay loam soils against the bedrock on hillsides.

The soils of the Santa Margarita Ranch viticultural area also include a series of sandy loam to loam soils in the floodplains of the creeks, which are abundant within the valley. They also include gravelly loam soils on the terraces and clay loams on the highest terraces and hillside as well as pockets of clay soils in some of the low-lying areas. The diversity of soil types reflects the landform age and the parent material type, which is largely Monterey Shale, as well as, its own eponymous Santa Margarita sandstone. A curiosity in the region lies within the Santa Margarita Ranch at the Oyster Ridge where large, fossilized oyster shells are as abundant as stars in the sky. This is reflective of an ancient shallow seabed that allowed oysters to thrive into exceptionally large specimens.


The Santa Margarita Ranch is approximately 18,300 acres at the southernmost point of the Paso Robles AVA and is considered a cool region II climate zone. With pronounced maritime and orographic influences, it receives approximately 29 inches of rain on average each year. The area is characterized by the high steep mountain slopes of Santa Lucia Range that drop dramatically down to the valley floor of the Salinas River. It has a very diverse bedrock and a diversity of soil types that sets it apart from the other Paso Robles AVAs. Visually stunning with an oak savanna in the valley floor to chaparral and mixed woodlands on the hillslopes above and many creeks and streams that cut the landscape, the Santa Margarita AVA is quite something to behold. It’s no wonder it was identified by settlers as a place to establish an early agricultural and commercial hub.

Photo and video credit:  Ancient Peaks Winery and Acacia Productions