You probably should have posted this in the Southern California board, because no one outside So Cal knows where Topanga Canyon is.
For the sake of those who are outside California, during the deluge the last couple weeks a massive boulder slid off of a slope and onto Topanga Canyon Road, which is the main artery from LA's San Fernando Valley to Malibu.
The url below has a nice picture:
http://lauren.vortex.com/archive/000116.html