Nestled in the southeastern section of Sonoma County, California, within the North Bay area of the San Francisco Bay vicinity, lies the picturesque Sonoma Valley AVA. This region is celebrated as the cradle of California’s wine-making legacy, boasting some of the earliest established vineyards and wineries in the state. Despite challenges like the phylloxera infestation in the 1870s and the prohibition era in the early 20th century, the area’s viticultural heritage has persevered. Nowadays, its wines gain distinction through the designation of Sonoma Valley AVA and Carneros AVAs (American Viticultural Areas) by the United States government.
Sonoma Valley AVA is also a hub of cultural and recreational activities, hosting an array of events and festivals throughout the year, including the esteemed Sonoma International Film Festival. Landmarks such as the Quarryhill Botanic Garden, Mission San Francisco Solano, Jack London State Historic Park, Sonoma State Historic Park, and the historical Blue Wing Inn, dating back to 1840, are key attractions that draw visitors.
Geographically, Sonoma Valley is framed by the Mayacamas Mountains to the east and the Sonoma Mountains to the west. It extends from the San Pablo Bay in the south up to Santa Rosa in the north, with the Sonoma Creek meandering through the valley towards the bay. The region encompasses the city of Sonoma, parts of Santa Rosa, and a collection of unincorporated communities such as Kenwood, Glen Ellen, El Verano, Boyes Hot Springs, Fetters Hot Springs, and Agua Caliente, each with its unique charm.
Historically, this land was inhabited by the coastal Miwok, Pomo, and Wintun tribes, known to them as the “Valley of the Moon,” a name steeped in their folklore. The Spanish Franciscan missionaries selected this valley for the construction of Mission San Francisco Solano in 1823, the northernmost mission in their Alta California network, dedicated to St. Francis Solanus. This marked the beginning of profound changes in the area. Under the independent Mexican rule, the mission system was secularized, and the town of Sonoma was established by General Mariano Guadalupe Vallejo, following the Mexican urban layout centered around the now-historic plaza.
Known also as the “Valley of the Seven Moons,” the area witnessed significant historical events like the raising of the first California Bear Flag and the founding of the Bear Flag Republic, with Vallejo playing a pivotal role in the region’s transition into American statehood in 1850. He was instrumental in shaping Sonoma’s development and in the establishment of renowned wineries such as Buena Vista Winery and Gundlach Bundschu.
Later, communities like Kenwood, Glen Ellen, Schellville, and Boyes Hot Springs emerged, many evolving around the natural geothermal springs, becoming fashionable health retreats until the mid-20th century. Presently, places like the Sonoma Mission Inn in Boyes Hot Springs continue to draw visitors. The area’s wineries, historical landmarks, and natural splendor remain central to its appeal.
However, Sonoma Valley AVA has not been immune to challenges. In October 2017, it faced significant devastation from the Tubbs Fire, marking a difficult chapter in its history. Despite this, the resilience and beauty of Sonoma Valley AVA endure, making it a cherished destination and an integral part of California’s cultural and natural heritage.
The moniker “Valley of the Moon” was first documented in a report to the California Legislature in 1850, penned by General Mariano Guadalupe Vallejo.
Jack London, a writer and ranch owner in the area, attributed the origin of ‘Sonoma’, a term meaning ‘valley of the moon,’ to indigenous language, a notion he embraced in his literary work titled identically. The interpretation of ‘Sonoma,’ however, is subject to various translations (refer to Sonoma County, California for more). The Miwok and Pomo tribes, indigenous to the valley, interpreted the term to signify either ‘valley of the moon’ or ‘a land of many moons.’ It’s speculated that early settlers might have misconstrued ‘many moons’ as ‘valley of moons.’ Miwok folklore describes the moon as emerging from or being cradled within this valley, with legends even suggesting the moon’s multiple appearances in a single evening.
Furthermore, the indigenous lexicon often includes the suffix ‘tso-noma,’ combining ‘tso’ (earth) with ‘noma’ (village), to denote ‘earth village.’ Another perspective traces ‘Sonoma’ back to the Patwin tribes located west of the Sacramento River, interpreting it as ‘nose’ based on the Wintu language. As reported in California Place Names, this interpretation aligns with an account by Padre Arroyo, which translates ‘nose’ as ‘sonom’ in the Suisun dialect. This name might have originated from a native chief known for a distinctive nose, with the term ‘Chief Nose’ possibly being extended to the surrounding land and its prominent natural features.
Geology
Nestled within the Coast Range Physiographic province, Sonoma Valley’s subterranean landscape is composed of the profound Great Valley Sequence — a tapestry of shale, sandstone, and conglomerate that came into being through sedimentation in a gradient ranging from continental slopes to abyssal plains, driven by turbidite currents. This intricate sequence from the Cretaceous period lies atop and converges with the Franciscan Complex at the Coast Range Thrust boundary. The Franciscan Complex, a product of the Jurassic-Cretaceous era, showcases a mosaic of contorted and elevated terrains, shaped by the subduction of the ancient oceanic Farallon Plate beneath the North American landmass. The region witnessed a phase of volcanic activity during the late Miocene-Pliocene epoch (approximately 10 to 4 million years ago), as evidenced by the Late Miocene Tolay Volcanics and the Late Miocene-Pliocene Sonoma Volcanics, which are intricately layered with the sedimentary deposits of the late Miocene-Pliocene Petaluma Formation. This formation, dating back approximately 9 to 4 million years, was characterized by a vibrant freshwater river network that coursed from east to west, weaving through the volcanic landscape.
In this dynamic geological era, volcanic eruptions spewed lava that intertwined with riverborne sediments, resulting in a complex layering of volcanic material and river deposits. The volcanic features of the region might have shared similarities with island arc systems. Traces of the Petaluma Formation stretch from Sears Point to Santa Rosa, skirting Sonoma Mountain and extending westward to Cotati, where it merges with the marine sandstone known as the Wilson Grove Formation. Interestingly, the gravels found within this formation didn’t originate from nearby Napa but were traced back to mountain ranges situated to the east of San Jose, California. This geological footprint doesn’t imply a northward river flow from San Jose to Sonoma; instead, it suggests that the strike-slip movements along the Hayward-Sonoma Valley-Carneros fault system have geologically repositioned present-day Sonoma County, distancing it northward from the mountains near San Jose where the basin initially formed.
Sonoma Valley’s landscape is sculpted by the Sonoma Creek, a waterway that originates in the verdant terrains of Sugarloaf Ridge State Park and journeys to meet the San Pablo Bay at the Napa Sonoma Marsh. The creek’s journey is enriched by the contributions of its significant tributaries, including Yulupa Creek, Graham Creek, Calabazas Creek, Bear Creek, Schell Creek, and Carriger Creek, each adding to the dynamic hydrological narrative of the valley.
Hydrogeology
During the spring of 2006, a detailed examination of groundwater resources within the Sonoma Valley AVA was carried out through a collaborative effort between the United States Geological Survey and the Sonoma County Water Agency. The outcomes of this extensive study are available for public access on the website of USGS publications. Presently, a dedicated Basin Advisory Panel, representing a diverse group of participants including agricultural sectors, environmental advocates, owners of domestic wells, city administrations, and governmental bodies, is actively engaged in formulating a strategic plan aimed at safeguarding the groundwater reserves in the region.
