Any ID beyond "Cereus"?

[Lair3514]

Pictures hard to get because this cactus established itself within the sheltering branches of a mesquite tree. I've walked by this tree in past without noticing its guest/intruder! I lingered taking pictures and owners came out and offered it's "one of the Cereus." They said it is a fast grower. They estimated it grew this much in five years. They didn't plant it. Said a seed must have been deposited by bird. Currently cactus has single stem. Here's the pictures. Thanks for ID help, if possible.

[Christer Johansson]

What about Cereus hildmannianus?
http://commons.wikimedia.org/wiki/Cereus_hildmannianus

[GermanStar]

Looks like your run of the mill Peruvian from here. No?

[Lair3514]

Thank you, Christen and GS. I should have known but I continue to be baffled by the range of plants called Cereus peruvianus (your website, Christen, gave hildmannianus and peruvianus as synonyms). Small, medium or large: most of the white-flowered night bloomers in neighborhood seem to be Cereus peruvianus. I appreciate your help.

Edit: Further reading and picture browsing left me with a resolution. Though Echinopsis pachanoi and peruviana (not surprisingly) look similar to Cereus peruvianus and hildmannianus, it is best to accept Cereus peruvianus with a big asterisk.

[GermanStar]

No doubt, which is why I deferred to 'Peruvian'. In this instance, common name might be a better choice.