Cima volcanic field is a volcanic field in San Bernardino County, California, close to the border with Nevada. The volcanic field covers a surface area of within the Mojave National Preserve west of the Cima Dome and consists of about 40 volcanic cones with about 60 lava flows. The volcanic cones range from simple cones over multi-cratered mountains to eroded hills, and lava flows are up to long. At least one lava tube exists in the field and can be visited.
Volcanic activity in the field commenced in the Late Miocene and after a pause between 3 and 1 million years ago continued into the latest Pleistocene. The youngest cone is known as the Black Tank cone and formed about 15,000 years before present, although it is possible that it was formed through two separate eruption events; formerly it was considered to be of historical age.
Geography and geology
The Cima volcanic field lies in the eastern Mojave Desert of California, between the Shadow Valley in the northeast, the Cima Dome in the east and the Soda Lake Valley in the southwest. Southwest of the field is Kelbaker Road which crosses some lava flows, and dirt roads such as the Indian Springs Trail and the Aiken Mine Road crisscross between the volcanoes.
Interstate 15 passes north of the field and just south of older volcanic units, while California State Route 127 runs west and southwest of the field, The city of Las Vegas is northeast of the area. The Cima volcanoes are part of the Mojave National Preserve and since 1973 they make up the Cinder Cones National Natural Landmark.
During the Holocene and until recent times, humans engraved petroglyphs into the lava flows. One cinder cone was quarried to obtain materials for road construction. The volcanic field has been the subject of soil sciences and landscape development research.
Regional
Volcanism is widespread in the western United States and occurs in various forms at various places. Among the better known are the Cascade volcanoes created by subduction off the western coast of North America, which include the caldera of Mount Mazama (created by a large eruption in the early Holocene) as well as stratovolcanoes such as Mount St. Helens and mafic volcanic fields. Other volcanic centres in the United States are those associated with Yellowstone Caldera and Snake River Plain, those along the margins of the Colorado Plateau, volcanoes linked to the Rio Grande Rift and Jemez lineament, and finally volcanoes in the western Basin and Range Province such as the Cima volcanic field.
Generally, volcanic activity was widespread in the dry regions of the western United States during the Tertiary and Quaternary, forming several volcanic fields. An earlier phase of felsic volcanism during the Tertiary was followed during the Quaternary by more basaltic volcanism, often in the form of short-lived volcanic vents. Examples of this kind of volcanism are the Cima volcanic field, the San Francisco volcanic field (Arizona), the Southwest Nevada volcanic field (Nevada) and the Zuni-Bandera volcanic field (New Mexico).
The Cima volcanic field is part of the Mojave Desert, which in turn belongs to the Basin and Range Province and features both mountains exceeding height which trend in southeast–northwest direction, with broad valleys between the mountains.
Local
There are about 40 cones in the Cima volcanic field. The cones are as much as wide and high, and are concentrated between elevations of on a south-southwest tilting slope. Some cones are well preserved with intact craters, while others have been reduced to hills by erosion. Some cones have more than one crater. North of the main field lie two outcrops of older volcanic rocks (Miocene to Pliocene); other than this separate older outcrop volcanic activity appears to have occurred without any preferential alignment. Several washes such as Willow Wash, Black Tank Wash and Indian Creek cross through the field and have eroded lava flows.
The youngest cone () in the southwestern part of the field is called Black Tank cone. The Black Tank cone is the source of a long lava flow, which at first forms a levee-bound channel and then narrows out into a lobate shape. It also shows traces of a lava tube and has a volume of . This flow may have been preceded by a previous lava flow which was later buried by the main flow. An older vent lies just south-southwest of the Black Tank Cone.