Help with Inventory with 2 distribution centers please

[dermaganix]

Essentially we will have two distribution points one on each coast of the US.  I have defined the two warehouses, I understand how to add inventory to each and transfers between etc.  My concern is how do I define where the inventory is pulled and shipped from to keep the correct inventory at each location and for each location to understand when the order applies to them.  Essentially both distribution warehouses will be assigned half of the US basically each warehouse will have a defined group of states that applies to it.  How do I define this and obviously shipping should be based off the warehouse that it is shipping from, any insights on this would be greatly appreciated.