I had been observing this plant from a far for almost a couple years now. Off and on when I travel in the bus that took this route, I would turn my head at the window seat, and my gaze would fall on this huge plant that seemed to be significantly towering over all the other plants that the gardener grew round it. A couple of months ago I noticed a huge spike that grew .... and slowly it did grow huge almost 4 stories high. It was after one of my tea time with dear husband around the neighborhood that I finally got a chance to inch close up on this plant. It's pretty amazing ..... many of my gardening friends couldn't help but commented on this beauty when I shared the photos here at a social networking site :-)
According to a friend the ID is Agave atrovirens . It may have taken 40 years for the plant to grow this size big. After flowering, the mother plant will produce hundreds of offsets and then it will slowly die off. Such is the cycle in nature to propagate the plant.