Characteristics of active faults in the Central Coast Ranges of California, with application to the safety of Dams*

ABSTRACT The California Coast Ranges mercury deposits are part of the western North America mercury belt, in which mercury occurs most commonly as red cinnabar (α-HgS), sometimes associated with its high-temperature polymorph, metacinnabar (β-HgS). In the Coast Ranges, ores were deposited from hydrothermal solutions and range in age from Miocene to Holocene. Ore deposition at Mount Diablo generally occurred along active faults and associated extension fractures in the Franciscan complex, most often in serpentinite that had been hydrothermally altered to silica-carbonate rock. The Mount Diablo mine lies ~48 km (~30 miles) northeast of San Francisco in Contra Costa County and is mineralogically unique in California, because metacinnabar, the higher-temperature polymorph of mercury sulfide, is a major primary ore mineral in the deposit, while at all other mercury mines in California, it is quite rare. In addition, hydrothermal activity is so recent that sulfurous gases and methane continued to be released into the mine at least into the 1940s. Historically, long before active large-scale mining began in the 1800s, the Mount Diablo mercury deposits were known to the Indigenous people of the Ohlone tribes, who used the cinnabar in rituals as well as for red pigment to decorate their bodies, and as a prized trade item. The deposit was later rediscovered in 1863 and mined intermittently until 1958. The Mount Diablo mine and adjacent Rhyne (also variously spelled Ryne or Rhine) mine were the sites of most of the mercury operations in the region, and at both mines, mercury ore occurs in structurally controlled lenticular bodies of silica-carbonate rock and serpentinite. The total district production probably exceeded 12,300 flasks (at 76 pounds or ~34.5 kg per flask) at an estimated grade of 2711 g per metric ton. Low-grade ore reserves are believed to still exist, with 17,000 short tons of indicated and inferred ore. Other minor deposits of copper, silver, and gold occur on Mount Diablo, principally in and around Eagle Peak, but mercury is not associated with these deposits.

Download Full-text

Seismic images of the deep structure of the San Andreas Fault System, Central Coast Ranges, California

Journal of Geophysical Research Atmospheres ◽

10.1029/jb086ib06p05039 ◽

1981 ◽

Vol 86 (B6) ◽

pp. 5039-5052 ◽

Cited By ~ 36

Author(s):

George Zandt

Keyword(s):

San Andreas Fault ◽

Deep Structure ◽

Fault System ◽

Central Coast ◽

San Andreas ◽

San Andreas Fault System ◽

Coast Ranges ◽

Seismic Images

Download Full-text

Silvicultural Approaches to Develop Northern Spotted Owl Nesting Sites, Central Coast Ranges, Oregon

Western Journal of Applied Forestry ◽

10.1093/wjaf/20.1.13 ◽

2005 ◽

Vol 20 (1) ◽

pp. 13-27 ◽

Cited By ~ 6

Author(s):

Lawrence S. Andrews ◽

John P. Perkins ◽

James A. Thrailkill ◽

Nathan J. Poage ◽

John C. Tappeiner II

Keyword(s):

Tree Planting ◽

Stand Age ◽

Central Coast ◽

Forest Patches ◽

Individual Tree ◽

Spotted Owl ◽

Nest Sites ◽

Spotted Owls ◽

Nesting Sites ◽

Coast Ranges

Abstract The life-history requirements of northern spotted owls (Strix occidentalis caurina), a federally listed “threatened” species, are associated with late-successional habitats. Nesting sites are an important habitat requirement for spotted owls. We used an individual-tree, distance-independent growth model to explore a range of management scenarios for young Douglas-fir stands (age class 50 years) and estimated which scenarios promoted the development of forest patches that emulate the species mix and diameter distributions at known spotted owl nest sites in the central Coast Ranges of Oregon. Our modeling indicates that without silvicultural intervention or natural disturbances, the young stands (170–247 trees/ac) investigated did not develop features associated with spotted owl nest sites within 160-year total stand age. Silvicultural simulations that modeled heavy thinnings at ages 50 and 80 years, followed by tree-planting and additional thinnings developed forest patches structurally similar to our sample of spotted owl nest sites. We infer that silvicultural activities in federally managed, late-successional reserves may need to include alternatives beyond the scope of those permitted under current land use guidelines to accelerate the development of stand structures that better meet the nesting site requirements of spotted owls. West. J. Appl. For. 20(1):13–27.

Download Full-text