Sonoma County is located in the U.S. state of California. As of the 2020 United States Census, its population was 488,863. Its seat of government and largest city is Santa Rosa.
Sonoma Valley is a valley located in southeastern Sonoma County, California, in the North Bay region of the San Francisco Bay Area. Known as the birthplace of the California wine industry, the valley is home to some of the earliest vineyards and wineries in the state, some of which survived the phylloxera epidemic of the 1870s and the impact of prohibition in the early 20th century. Today, the valley's wines are promoted by the U.S. federal government's Sonoma Valley and Carneros AVAs.
The Coast Ranges of California span 400 miles (644 km) from Del Norte or Humboldt County, California, south to Santa Barbara County. The other three coastal California mountain ranges are the Transverse Ranges, Peninsular Ranges and the Klamath Mountains.
The Mendocino Range is one of several coastal mountain ranges which compose the Pacific Coast Range. This massive range of coastal mountains was formed during a period of coastal orogeny, millions of years ago. The Mendocino Range is a component of the California Coast Ranges of California. The Klamath Range is north of this region, and the Cascade Range runs to the northeast.
Putah Creek is a major stream in Northern California, a tributary of the Yolo Bypass, and ultimately, the Sacramento River. The 85-mile-long (137 km) creek has its headwaters in the Mayacamas Mountains, a part of the Coast Range, and flows east through two dams. First, Monticello Dam forms Lake Berryessa, below which Putah Creek forms the border of Yolo and Solano Counties, and then flows to the Putah Diversion Dam and Lake Solano. After several drought years in the late 1980s, the majority of Putah Creek went dry, prompting a landmark lawsuit that resulted in the signing of the Putah Creek Accord in 2000. The Accord established releases from the dams to maintain stream flows in Putah Creek, with natural flow regimes which spike in winter/spring and ebb in summer/fall. The restoration of natural flow regimes has resulted in a doubling of riparian bird species and a return of spawning native steelhead trout and Chinook salmon, as well as protecting the livelihood of farmers on the lower watershed.
Crystal Springs Reservoir is a pair of artificial lakes located in the northern Santa Cruz Mountains of San Mateo County, California, situated in the rift valley created by the San Andreas Fault just to the west of the cities of San Mateo and Hillsborough, and I-280. The lakes are part of the San Mateo Creek watershed. Crystal Springs Regional Trail runs along the reservoir.
The Russian River is a southward-flowing river that drains 1,485 sq mi (3,850 km2) of Sonoma and Mendocino counties in Northern California. With an annual average discharge of approximately 1,600,000 acre feet (2.0 km3), it is the second-largest river flowing through the nine-county Greater San Francisco Bay Area, with a mainstem 115 mi (185 km) long.
Piner Creek is a stream in northeast Santa Rosa, California, United States which originates as an outlet of Fountaingrove Lake. Piner Creek discharges to Santa Rosa Creek which in turn joins the Laguna de Santa Rosa. The upper reaches in the foothills of the Mayacamas Mountains are at elevations of 200 to 300 feet, while the lower and middle reaches are located on the Santa Rosa Plain at elevations of between the 110- and 140-foot contours; therefore, these lower reaches have a gradient of about 1:250 toward the southwest. Geologic studies in the lower and middle reaches of Piner Creek indicate groundwater levels ranging from three to 15 feet below the surface. Prior to extensive urban development of the middle and lower reaches, the landscape earlier bore extensive agricultural uses including plum orchards, which fruit was subsequently processed for prunes.
Calabazas Creek is a 5.5-mile-long (8.9 km) stream in the Sonoma Valley, California, United States, that rises in the southern Mayacamas Mountains and empties into Sonoma Creek near Glen Ellen.
The Clear Lake Volcanic Field is a volcanic field beside Clear Lake in California's northern Coast Ranges. The site of late-Pliocene to early Holocene activity, the volcanic field consists of lava domes, cinder cones, and maars with eruptive products varying from basalt to rhyolite. The site's threat level is ranked "High" at #33 in the top volcanic threats in the United States according to "2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment". The last eruption was about 11,000 years ago. Cobb Mountain and Mount Konocti are the two highest peaks in the volcanic field, at 4,724 feet (1,440 m) and 4,285 feet (1,306 m) respectively.
The Geysers is the world's largest geothermal field, containing a complex of 18 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains approximately 72 miles (116 km) north of San Francisco, California.
Mark West Creek is a 29.9-mile-long (48.1 km) stream that rises in the Mayacamas Mountains of Sonoma County, California, United States. Tributaries of Mark West Creek include Porter Creek and Hummingbird Creek, both of which originate in the same mountain range. Discharge waters of Mark West Creek reach the Russian River after a confluence with the Laguna de Santa Rosa. The Community Clean Water Institute has developed a program for monitoring pollutants in Mark West Creek.
Cobb Mountain is the tallest mountain in the Mayacamas Mountains of California.
Big Sulphur Creek is a westward-flowing stream in northern Sonoma County, California, United States, which springs from The Geysers in the Mayacamas Mountains and runs 20 miles (32 km) to empty into the Russian River.
Rancho Los Guilicos was an 18,834-acre (76.22 km2) Mexican land grant in present-day Sonoma County, California given in 1837 by Governor Juan B. Alvarado to John (Juan) Wilson. The grant extended along Sonoma Creek, south of Santa Rosa from Santa Rosa Creek south to almost Glen Ellen, and encompassed present day Oakmont, Kenwood and Annadel State Park.
The Howell Mountains, which are also known as the Mt. George Range, are one of the California Coast Ranges. They divide the Suisun Valley on the east side, from Napa Valley on the west. Historically the southern part of the range has been referred to as both the Sierra de Suscol and as the Sierra de Napa.
Kelsey Creek is a watercourse in Lake County, California, United States, that feeds Clear Lake from the south. Originally forest-covered, the watershed has been converted in the lower parts to farmland and for urban use. Higher up, the forests have been cleared, regrown, and cleared again. The northern part of the creek flows through a geothermal field that feeds power plants and hot springs. The wooded Cobb area in the higher part of the watershed was once home to resorts as early as the 1850s.
Harbin Mountain is a mountain in Lake County, California. It may be seen as a high point on a spur of Boggs Mountain or as a connected mountain to the southeast of Boggs Mountain.
Cow Mountain Ridge is a ridge in Lake County, California, and Mendocino County, California. It joins Cow Mountain from the south.
Mahnke Peak is a 3,652 feet (1,113 m) mountain in Mendocino County, California.
