Thank you very much for awnsering my query; it is all very interesting. I believe I had heard that "mendi" was Basque for "mountain", but I didn't know that "ota" was the name of a tree. I suppose you must know the Basque language; I have heard it is a very difficult language to learn because it is in no way similar to any other European tongue.
I live in México and Basque ancestors were from central México, mainly the State of Guanajuato. I have read that the Otamendi surname comes from the province of Güipozcua in the Basque Country and that my ancestors were Pérez de Otamendi, but that's pretty much it. Other Basque surnames in my family include Heredia, Olace, and presumably Ruiz de Chávez and Infante de Chávez. Olace is not a toponimic nor a patronimic, but suposedly some kind of title carried by the "Condes de Olace", or so I read in an encyclopedia.
Well, thanks a lot for the info! By the way; any relation to Pedro Armendáriz, the Mexican actor?