Alex said:Is this Cottonwood you are talking about the same as Poplar?
It is in the same family, but cottonwood here in Minnesota has no shape, form, color, or grain. While a hardwood, it is very soft. It is almost difficult to work, like trying to turn cork or something. As light as it is, has no btu value for heating either. If it were used on an outside wall as you say your cabin is, it would rot down to dust in 5 years or so. A very different wood than poplar.
Having said that, my unckle had 10 100' plus cottonwoods 42" across. He had one sawn 40-50 years ago, and used some of the wood for rafters on a steer shed. Somehow, it's still standing. 10 years ago, even he was shaking his head at that, how it's ever held up.