Pressure treated (PT) lumber is the predominant wood material used in San Francisco landscapes where the exposure will be in a wet enviorment or when there is earth/wood contact. Its identified by a greenish or very brown color with staple size slits on all surfaces except the ends. PT lumber is basically a douglass fir or equivalent lumber that has been infused with preservatives. The preservative used until 2004 for home applications was CCA or chromated copper arsenate with the arsenate component being highly toxic and a known carcinogen. Today we use PT that has been infused with amine copper quat (ACQ) or copper azole (CA) or micronized copper quatemary (MCQ), all products without the arsenate and much safer. Does that mean we would recommend building a raised vegetable planter out of it? Although the manufacturer says its safe, we still would not recommend it. But we at Tamate Landscaping do use it for the structural components of decks and fences since its the most economical and will last the longest. Still there are some options in some applications. For example, instead of a PT retaining wall, consider concrete. Or for fences, consider all redwood instead of PT structural components. These options will cost much more but they are options none the less. Do your own research regarding these products and feel free to contact us for different options for your specific application.