formula to choose list

Is there a way in XL 2007 to make a formula that chooses a list to use as a drop down. For instance I have 3 office locations (LV, CA, UT) and I have X number of employees at each location. If I make 3 lists titled each location of the employees, is there a formula I can create that says IF cell A2 (random cell with location name) is CA then use list CA and it would produce a drop down with that employee list. I know that generally for lists you have to specify in validation what list to use. I have seen workbooks where on one page you make a selection from a drop down and it makes a drop down on another page specific to the initial choice but I have no idea how its been done. Help...