When you build a new California deck, the lumber must be allowed to acclimate for several weeks in conditions similar to where your deck will be installed. A completed deck will be exposed to the environment, and the acclimation process is what prepares the boards to deal with those conditions. You would not construct your deck in a shed or cover the finished deck with a tarp, so why would you do that to the boards? Instead, stack your boards outdoors with spacers in between each level, allowing for lots of ventilation across every surface of each board. Non-acclimated lumber will warp, buckle, and check.