What is sawn treated wood used for?

"Treated" lumber COULD have several meanings, but it usually means treated to resist rot and attack by insects. Early treatments included creosote (thin railroad ties). "Green" lumber was treated with Chrome, Copper, and Arsenic. Due to health hazards, wood a consumer would be likely to come in contact with (handrails, etc) are now treated with a Copper Boron mix. These woods are used for outdoor stairs, decks, docks, gazebos, etc.- anywhere you would have direct contact with the ground.

In Hawaii, the Formosa Termite can do GREAT damage to lumber, so much of the house that is built in Hawaii uses treated lumber.