Yes, the desert gets quite chilly in the mornings and eves, but then it could get up into the 70's by noon even in October. I would probably wear a jacket that I could shred later, probably a sleeveless jersey underneath. Or what if you did short sleeve but got some arm warmers ? I've never used them but that could work. I'd wear knee-length pants in any case, but most important would be not to forget gloves, full-length ones. Hands get cold so fast !