I spent half my childhood in South Lake Tahoe and have lived in the region most of my life. During the 80's and 90's, much of which was a period of drought for the region, beetles were a problem and being actively mitigated by the forestry service. You can go through the national forest all through the sierras and see trees that have been tagged for removal due to beetles. The problem is very severe right now and certainly the worst I can remember. I've got a couple of friends that work for the us forestry service and they say it's so bad they can't keep up with it. Other sources point out that beetle infestation is part of the problem.
Local news site for Tahoe specifically: http://www.tahoedailytribune.com/news/california-tahoe-area-...
SF Chronicle on the beetle problem and commenting on the excess wood: http://www.sfchronicle.com/bayarea/article/California-has-66...