The Howell Mountains, which are also known as the Mt. George Range, are one of the

California Coast Ranges The Coast Ranges of California span 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. Ph ...

. They divide the Suisun Valley on the east side, from

Napa Valley Napa Valley is an American Viticultural Area (AVA) located in Napa County in California's Wine Country. It was established by the Bureau of Alcohol, Tobacco and Firearms (ATF) on January 27, 1981. Napa Valley is considered one of the premier ...

on the west. Historically the southern part of the range has been referred to as both the Sierra de Suscol (Suscol Hills) and as the Sierra de Napa (Napa Hills).

Geography

The Howell Mountains begin at Sulphur Springs Mountain, near the towns of Vallejo and

Benicia Benicia ( , ) is a waterside city in Solano County, California, located in the North Bay region of the San Francisco Bay Area. It served as the capital of California for nearly thirteen months from 1853 to 1854. The population was 26,997 at th ...

, and just north of the

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

where the

Sacramento River The Sacramento River ( es, Río Sacramento) is the principal river of Northern California in the United States and is the largest river in California. Rising in the Klamath Mountains, the river flows south for before reaching the Sacramento–S ...

flows into

San Francisco Bay San Francisco Bay is a large tidal estuary in the United States, U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, California, San Jose, and Oakland, Ca ...

. The range then trends to the north and northwest for about to Howell Mountain, just northeast of St. Helena, California, where it merges with the

Mayacamas Mountains The Mayacamas Mountains are located in northwestern California in the United States. The mountain range is part of the Northern Inner Coast Ranges, of the California Coast Ranges System. Geography The Mayacamas Mountains are located south of th ...

. The

Vaca Mountains The Vaca Mountains are a mountain range in Napa and Solano Counties, California that is one of the California Coast Ranges. They represent the easternmost of the Inner Coast Ranges in north−central California, and divide the Suisun Valley o ...

, which are separated from the Howell Mountains by Suisun Valley on the east side, merge with the latter range northeast of St. Helena also. The crest of the range, which culminates at feet in the twin summit of Twin Sisters, represents the divide between the drainage of the

Napa River The Napa River is a river approximately long in the U.S. state of California. It drains a famous wine-growing region called the Napa Valley, in the mountains north of the San Francisco Bay. Milliken Creek and Mt. Veeder watersheds are a fe ...

on the west side, and Suisun and Green Valley Creeks on the east. Although Twin Sisters is the high point, both Howell Mountain and Mt. George to the north are better known, due to proximity to grape-growing regions that are popular tourist destinations.

Climate

The Howell Mountains have Mediterranean climate with a cool rainy winter, and a warm dry summer with high temperatures up to at lower elevations. Average annual rainfall ranges from per year at Howell Mountain in the north, to per year at Mt. George, to per year at Benicia in the south. Rainfall is similar on both the west and east sides of the range, with no noticeable

rain shadow A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its leeward side. Evaporated moisture from water bodies (such as oceans and large lakes) is carri ...

effect. Because gentle winds blowing inland from the estuary at

San Pablo Bay San Pablo Bay is a tidal estuary that forms the northern extension of San Francisco Bay in the East Bay and North Bay regions of the San Francisco Bay Area in northern California. Most of the Bay is shallow; however, there is a deep water c ...

and

Suisun Bay Suisun Bay ( ; Wintun for "where the west wind blows") is a shallow tidal estuary (a northeastern extension of the San Francisco Bay) in Northern California. It lies at the confluence of the Sacramento River and San Joaquin River, forming the ...

are common, hard frosts are very rare, which makes the lower slopes of the mountains ideal for growing grapes, olives and fruit trees.

Geology

Although

bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...

in most parts of the Howell Mountains is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

origin known as the Sonoma Volcanics, older sedimentary rocks of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

age Great Valley Sequence are found in the

area at the southern end of the range, and in the Lake Hennessey area to the east of

St. Helena Saint Helena () is a British overseas territory located in the South Atlantic Ocean. It is a remote volcanic tropical island west of the coast of south-western Africa, and east of Rio de Janeiro in South America. It is one of three constit ...

. The Sonoma volcanics, which make up bedrock in all of the grape-growing areas of the Napa Valley side, are late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

to early

Pleistocene The Pleistocene ( , often referred to as the '' Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed ...

in age, and made up largely of

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is o ...

-rich

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained ( aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The min ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s and

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

s interbedded with silica-poor

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

and

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

lava Lava is molten or partially molten rock ( magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

flows, with some volcanic

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classif ...

s that are related to

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

processes. Serpentine is found in a few places where older sedimentary rocks are faulted against younger volcanics, and in some of these same areas, particularly around Sulphur Springs Mountain at the southern terminous,

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of mercury(II) sulfide (HgS). It is the most common source ore for refining elemental mercury and is the historic source for the bri ...

deposits were mined in the late 1800s for quicksilver.

Agriculture and grazing

The west slope of the Howell Mountains is noted for its vineyards and wineries, which tend to be located where the soils are derived from rhyolite tuffs. Although rhyolitic rocks generally weather to

soils Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former term ...

that are considered to be nutrient poor, the Howell Mountain

American Viticultural Area An American Viticultural Area (AVA) is a designated wine grape-growing region in the United States, providing an official appellation for the mutual benefit of wineries and consumers. Winemakers frequently want their consumers to know about th ...

and other

wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are ...

appellation An appellation is a legally defined and protected geographical indication primarily used to identify where the grapes for a wine were grown, although other types of food often have appellations as well. Restrictions other than geographical boun ...

districts located on the west slope claim that grape vines planted in these soils are stressed and as a consequence produce wine grapes that are superior in quality for wine making when compared to grapes grown on unstressed vines planted in the richer

loams Loam (in geology and soil science) is soil composed mostly of sand (particle size > ), silt (particle size > ), and a smaller amount of clay (particle size < ). By weight, its mineral composition is about 40–40–20% concentration of sand–sil ...

of the valley floor. Despite the observation that volcanic soils on the east slope (Suisun Valley side) are similar to those on the west slope (Napa Valley side), cattle grazing predominates on the east slope and vineyards are few.

Origin of name

Although an 1842 Spanish land grant map clearly names the range of hills between the Suscol (Napa Valley) and Suisun Ranchos, and extending as far north as the Howell Mountain area as the "Sierras de Suscol" (Suscol Hills), this name is somewhat interchangeable today with "Sierra de Napa" (Napa Hills) and applies generally to the southernmost part of the range that looks down on the towns of Vallejo and Benicia. With the transformation of the northern Napa Valley into a premier wine-producing area and tourist attraction, names for the range such as the Howell Mountains and Mt. George Range that have more northerly derivations have become more popular. The fact that none of these names are recognized by the United States Geographical Survey means that the range has no official designation. Pioneer Isaac Howell and his family came to California in 1846. The family came to Napa Valley by 1848 and then settled up on the mountain which was part of Rancho Carne Humana by 1850 . Historians have argued over which Howell the mountain was named after---Isaac or his son John. Since both lived up there until 1868, people probably were referring to the whole group of Howells. Howell Mountain is named after John Howell, who, with a partner in 1856, opened at

the first

blacksmith A blacksmith is a metalsmith who creates objects primarily from wrought iron or steel, but sometimes from #Other metals, other metals, by forging the metal, using tools to hammer, bend, and cut (cf. tinsmith). Blacksmiths produce objects such ...

shop in

Napa County Napa County () is a county north of San Pablo Bay located in the northern portion of the U.S. state of California. As of the 2020 census, the population was 138,019. The county seat is the City of Napa. Napa County was one of the original c ...

. Howell Mountains was ultimately applied as well to the peaks to the south that separate Napa Valley from Suisun Valley. For example, Kunkel and Upson (1960) identify the Howell Mountains in their report on the geology and water resources of Napa County, and it is used similarly in other agricultural and geological publications, as well as by the wine industry, and in Napa County and Solano County reports. Because these mountains are not officially named, they are sometimes referred to as either the Mayacamas or

, which leads to confusion as the Howell Mountains for much of their extent are topographically and geologically distinct from adjacent ranges.

Notes and references

{{reflist , refs= {{cite book , author1=Hunt, Marguerite , author2=Gunn, Harry Lawrence , date=1926 , title=History of Solano County, California and Napa County, California, from their earliest settlement to the present time , chapter=History of St. Helena , publisher=S. J. Clarke Publishing Co. , location=Chicago , page=v. 1, chap. IV, p. 347 , no-pp=yes Elevations retrieved from the
search query
of the ''

Geographic Names Information System The Geographic Names Information System (GNIS) is a database of name and locative information about more than two million physical and cultural features throughout the United States and its territories, Antarctica, and the associated states of ...

'' of the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

. Retrieved 10 June 2013. {{cite web , title=Howell Mountain Region , url=http://www.howellmountain.org/about/region/ , website=Howell Mountain Vintners & Growers Association (website) , access-date=10 June 2013 {{cite book , author1=Graymer, R.W. , author2=Moring, B.C. , author3=Saucedo, G.J. , author4=Wentworth, C.M. , author5=Brabb, E.E. , author6=Knudsen, K.L. , date=2006 , title=Geologic Map of the San Francisco Bay Region , publisher=United States Geological Survey, in cooperation with the California Geological Survey , page=Scientific Investigations Map 2918 , no-pp=yes {{cite book , author1=Kunkel, F. , author2=Upson, J.E. , date=1960 , title=Geology and ground water in Napa and Sonoma Counties, California , publisher=United States Geological Survey, Water-Supply Paper 1495 , pages=4, 15–25 {{cite book , author1=Lambert, G. , author2=Kashiwagi, J.H. , date=1978 , title=Soil Survey of Napa County, California , publisher=United States Department of Agriculture, Soil Conservation Service Also, see {{cite book , author=Bates, L.A. , date=1977 , title=Soil survey of Solano County, California , publisher=United States Dept. of Agriculture, Soil Conservation Service, in cooperation with University of California Agriculture Experiment Station {{cite web , title=Llano del Suy-sun: Map of Rancho Suisun , date=1842 , url=http://content.cdlib.org/ark:/13030/hb08700292/ , publisher=U.S. District Court, California, Northern District , access-date=8 July 2013 Land case 162 ND, page 888; land case map D-361. Held at the Bancroft Library and available online a
Calsphere - University of California Collections for Educators
''Mt. George, California'' and ''Fairfield North, California'' 1:24,000 topographic quadrangles by the United States Geographical Survey. These maps provide information on the central part of the range, and adjacent quadrangles to the north and south provide additional information. California Coast Ranges Mountain ranges of Napa County, California Mountain ranges of Solano County, California Mountain ranges of the San Francisco Bay Area Mountain ranges of Northern California

Geography

Climate

Geology

Agriculture and grazing

Origin of name

See also

Notes and references