that have been particularly influential in survivalist circles are How to Implement a High Security Shelter in the Home by Joel Skousen, Rawles on Retreats and Relocation by James Wesley Rawles, and Life After Terrorism: What You Need to Know to Survive in Today's World by Bruce D. Clayton. Online survival websites, forums, and blogs (such as SurvivalBlog) discuss the best locales for survival retreats, how to build, fortify, and equip them, and how to form survivalist retreat groups. Economic troubles emerging from the credit collapse triggered by the 2007 U.S. subprime mortgage crisis have prompted a wider cross-section of the populace to modify their homes as well as establish dedicated survival retreats. James Wesley Rawles, the editor of SurvivalBlog was quoted by the New York Times in April 2008 that "interest in the survivalist movement 'is experiencing its largest growth since the late 1970s'”. He also stated that his blog's conservative core readership has been supplemented with "an increasing number of stridently green and left-of-center readers." Necessity for retreats Mel Tappan was quoted in 1981 by then AP correspondent Peter Arnett that: "The concept most fundamental to long term disaster preparedness, in retreating, is having a safe place to go to avoid the concentrated violence destined to erupt in the cities." Common retreat locale parameters Common retreat locale selection parameters include light population density, plentiful water, arable land, good solar exposure for gardening and photovoltaics, situation above any flood plains, and a diverse and healthy local economy. Fearing rioting, looting and other unrest, many survivalists advocate selecting retreat locales that are more than one tank of gasoline away from any major metropolitan region. Properties that are not in "channelized areas" or on anticipated "refugee lines of drift" are also touted. One of the key goals of retreats is to be self-sufficient for the duration of societal collapse. To that end, plentiful water and arable soil are paramount considerations. Beyond that, a priority is situation on isolated, defensible terrain. Typically, retreats do not want their habitations or structures jeopardized by being within line of sight of any major highway. Because of its low population density and diverse economy, James Wesley Rawles and Joel Skousen both recommend the Intermountain West region of the United States as a preferred region for relocation and setting up retreats. Although it has higher population density, Mel Tappan recommended southwestern Oregon, where he lived, primarily because