Oil Derrick

How could I not know what an oil derrick is? I came across a mention in a fiction novel I was reading, and made note to look the word up later. Oh, that is what those things are called. They are all over Long Beach. I remember listening to the clunk, clunk, clunk sound falling to sleep while on the streets. Think I was dreaming. Can not figure out exactly where I was sleeping when I listened to the rhythmic sounds. Perhaps I am thinking of hearing the drills as I walked around scooping out potential places to sleep. Or remembering jumping at the sounds hearing it after dark when Dawn & I walked around the rim of Signal Hill. Took photo of one of those during a recent walk to visit Hilltop Park.