Approximately 70% of the abandoned mines recorded servicewide are located in 22 of the NPS units within the Pacific West Region (PWR). The vast majority of these, however, are found in the State of California and neighboring Nevada, with Death Valley, Mojave, Lake Mead, and Joshua Tree having by far the highest numbers of mines in the NPS. Precious and semi-precious metals and industrial minerals have been the predominant commodities removed from the hardrock mines in the PWR. Although gold and silver mining typically attract the most attention, vast amounts of copper, tin, tungsten, talc, borates, and iron have also been extracted from what are now units of the NPS.
Despite the existence of both physical safety and environmental hazards at the numerous abandoned mines across the region, these sites have remained popular destinations for tourists and indeed are often interpreted to the public. Both individually and collectively these mines attract considerable interest because they preserve a portion of the history of the settlement of the West and represent the American dream of striking it rich. The PWR, like the rest of the NPS, must contend with managing numerous abandoned mineral lands (AML) that have historic value and preserve important wildlife habitat but also pose significant physical safety risks to the visiting public and park staff. Although there is a large range of possible treatments available to mitigate the hazards at abandoned mine features, the challenge is to devise treatments that can be installed in ways that accommodate their use as habitat for wildlife and, to the extent possible, minimize impacts on historic fabric and the visual character of cultural landscapes.
Congressional set asides in 2008 and 2009 provided funding for the mitigation of physical safety hazards at nearly 100 AML features at Joshua Tree, Mojave, Point Reyes, and Death Valley and represented the first major influx of funding to be applied to the problem in recent decades. Using funding made available as a result of the American Recovery and Reinvestment Act (ARRA) totaling nearly $13 million, 12 PWR parks were able to reduce physical hazards at over 600 AML features. In addition, extensive pre- and post-installation bat surveys were conducted at three parks and an AML inventory and assessment program affecting all of the NPS units in California was established through a cooperative agreement with the State of California's Abandoned Mine Lands Unit that serves as a major component of the current servicewide AML inventory and assessment effort. That project will be completed by the end of FY2013 and the results of that endeavor will then be reported as a supplement to the present report.
The extremely short time span allowed for obligation of funds under ARRA and the various unique rules attached to those funds created a number of obstacles for carrying out the best possible set of mitigation measures in all cases. Still, an unprecedented number of hazardous features were treated and a great deal was learned from the experience. Having developed a set of drawings and specifications for 18 of the most common mine closure types based on a wide range of experienced practitioners in the AML field, it is now possible to more readily identify an appropriate closure type for most applications, even though each must be modified to meet specific feature conditions. More difficult is the determination of which specific type of closure will best accommodate continued use of the feature by bats —a hotly debated topic among bat experts nationwide. Far more post-installation research on the effects of different supposedly batfriendly closures needs to be undertaken to resolve some of these questions.
From the perspective of historic preservation, the ARRA effort made it clear that it is far easier to avoid impacts to historic fabric in the installation of safety mitigation closures than it is to avoid impacts to the visual character of the cultural landscapes to which the features contribute. The questions of bat biology and preservation of the feel of an historic mine site are actually interconnected, as the use of above ground cupolas designed to accommodate bat use in some applications does more to impact the cultural landscape than if the closure were set into the feature to reduce its profile. Additional sound bat research would assist in the process of determining what sorts of closure types are indeed necessary to accommodate bat ingress and egress.