A Organ Pipe Cactus Wall: an elegant wall for a desert garden. This looks to be Organ Pipe Cactus (Lemaireocereus marinates) and a little research shows that it has often been used for natural fencing in the past. You can find more information through this Google Search on Organ Pipe Cactus.
Pots with succulents at entry stairs from street by David Feix Landscape Design, via Flickr :: if I ever get to live back in SoCal or out in Palm Springs, I'd have a cactus and succulent garden for sure. so gorgeous