It is located at the southernmost boundary of the 609,673 acres (953 sq mi) Paso Robles viticultural area nestled against the Santa Lucia Mountain Range and distinctly isolated from the other ten sub-appellations established on the same day.

Syrah has played a pivotal role in the AVA, with Cabernet Sauvignon, Zinfandel, Merlot, Pinot Noir and Chardonnay also featured in its grape inventory.

The northern portion of the Santa Margarita Ranch viticultural area boundary follows a combination of a land grant line, roads, and section lines that approximately delineate the northernmost extent of the Santa Margarita Land Grant region that is suitable for viticultural development, while excluding the urbanized areas of Atascadero to the north and the rugged terrain to the northeast.

The terrain to the east of the boundary is steep and rugged, and the region to the southeast includes terraces, benches and a generally flat valley floor.

Santa Margarita Ranch today remains one of California’s oldest historic sites, beginning with the Chumash and Salinan peoples who for more than 10,000 years they called this valley their home.

The padres were intrigued and finally accompanied the natives over the Cuesta Grade in 1774, and they found the beautiful Santa Margarita valley.

The rock and adobe walls of Asistencia still stand today used as a storage barn on the ranch and commomly referred as San Luis Obispo County’s "third mission.

A building was erected on the sightly bench of land in the lovely valley northeast of the Santa Lucia Range, about eight miles (13 km) north of San Luis Obispo and dedicated to its patroness, Santa Margarita, but it was only a branch of the mission of San Luis Obispo de Toloso, and under its management.

The walls of rough stone and cement, a coarse inartistic structure, still stand, interesting as a reminiscence of the past and picturesque as a ruin of one of the sacred edifices of early California.

Walter Colton refers to this as built for a granary of one of the ranchos cultivated by the good Father Martinez, of San Luis Obispo, and that it was usually well filled with grain.

In 1847, John C. Frémont marched through, arresting ranch owner Joaquin Estrada on his way to attack the Mexican army in Santa Barbara.

The tract has always been celebrated for its fertility ever since the Franciscan missionaries began to till its soil and establish warehouses to contain the extraordinary crops of frijoles, garbanzos, maiz, and other esculents.

Later on, when the Mexican lords of the manor reigned at Santa Margarita, the place was given up to the support of great herds of horned cattle, and agriculture was neglected.

In time the long-horned Mexican cattle have been replaced by better breeds, but still the greater part of this unequaled valley is devoted to beef raising.

The valley floor, at approximately 1,100 to 1,200 ft (340–370 m)} in elevation, includes a nearly flat landscape with gradual inclines and some hills to the north near the town of Santa Margarita.

Vineyards within the Santa Margarita Ranch viticultural area are planted primarily on the valley floor, across gently rolling terraces and perched above the creek beds.

As compared to the Templeton Gap District and Paso Robles Willow Creek District viticultural areas to the north, the growing season in the Santa Margarita Ranch viticultural area is less affected by the marine influence entering the Paso Robles region through the Templeton Gap.

Over time, these faults are largely responsible for the rare array of soil types: rock alluvium, granite, volcanic, shale and ancient seabed, that are visible to the naked eye.

In order to prevent overly vigorous growth in the fertile soils, vines are spaced closely together to promote root competition, and water is carefully managed.

The winery is renowned for its Cabernet Sauvignon, Zinfandel, Oyster Ridge Bordeaux-style blend and other wines that reflect the unique character of this sustainably farmed estate.