HI, although different spiecies may be more or less stable I would take a really good look at the grain. Did you ever see a tree leaning in the forest? Well there is an awfull lot of tension in a piece of lumber cut from a tree like that. You want a nice straight grained piece with no run out of the grain. The relitive wheight of a piece of wood can also be an indicator of dryness (lighter is better). One other thing you will often find on smaller dimensioned lumber (2x4) is that the pith runs somwhere down the middle of your board. The pith is the center of the tree when it was just a sapling and is unstable. I have found some beautifull vertical grained 2x6s over the years but they are few and far and getting farther. Smaller faster growing trees make course grained unstable wood. Take your time and pick through the pile. Some yards carry better graded material than others and keep it dryer. Just remember it is a privlige to be able to pick through a lot of material so please try to restack neater than you found it. Look for a good one, Steve.