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Mount Konocti / k oʊ ˈ n ɒ k t aɪ / is a volcano in Lake County, California on the south shore of Clear Lake. At 4,305 feet (1,312 m), it is the second highest peak in the Clear Lake Volcanic Field , which consists of numerous volcanic domes and cones ranging from 10,000 to 2.1 million years old.
Geologic map of the Clear Lake Volcanic Field. 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. [2]
Mount Saint Helena (Wappo: Kanamota, "Human Mountain") [4] is a peak in the Mayacamas Mountains with flanks in Napa, Sonoma, and Lake counties of California. Composed of uplifted volcanic rocks from the Clear Lake Volcanic Field , it is one of the few mountains in the San Francisco Bay Area to receive any snowfall during the winter.
The site's threat level is ranked "High" at #33 in the top volcanic threats in the United States in 2018 Update to the United States Geological Survey National Volcanic Threat Assessment. Cobb Mountain and Mount Konocti are the two highest peaks in the volcanic field, at 4,724 ft (1,440 m) and 4,285 ft (1,306 m) respectively.
The hills lie at the foot of Mount Konocti, a volcano which last erupted 11,000 years ago, but which is still regarded as active. [5] The terrain is rolling hills with elevations between 1,400 feet (430 m) and 3,000 feet (910 m) above sea level. Red Hills receives an average of 25 to 40 inches (635–1,016 mm) of rainfall annually. [1] [3]
There are numerous small faults present in the south end of the lake as well as many volcanoes, ranging in age from 10,000 to 2.1 million years, the largest being Mount Konocti, sitting at the middle of the lake's south shore. There have been no eruptions from the Clear Lake Volcanic Field for thousands of years, but there are indicators ...
Like nearby Mount Saint Helena, Cobb Mountain is tall enough to receive winter snowfall. [3] The mountain has a sub-peak referred to as Cobb Mountain – Southwest Peak with an elevation of about 4483+ feet, (1367+ m) NAVD 88 ; [ 4 ] Southwest Peak lies on the Sonoma -Lake county line and is the highest point in Sonoma County.
The Alexandra Volcanic Group (also known as Alexandra volcanic lineament or Alexandra Volcanics) is a chain of extinct calc-alkalic basaltic stratovolcanoes that were most active between 2.74 and 1.60 million years ago but is now known to have had more recent activity between 1.6 and 0.9 million years ago. [1]